Almost nothing! No matter what Holy Book you look in, pretty much none of it is true. Yes, some things did happen, but that's mostly human history. 99% of the lore on God and his angels was wrong. In fact, angels don't even call themselves 'angels,' and claim that it's just a title that humans made up. Their real title can't be said with a human tongue, and their real visage can't be perceived by humans, either.
So, if none of that is right, then what are angels?
Angels (ἄγγελος, מלאך, ملائكة), as we call them, are not messengers. They are not peaceful, nor are they meant to protect humans. They do not act as guides, either. Angels, for the most part, just observe everything that happens and carry out "God's" will. They are capable of battle, but not in the way we would imagine a battle. Entire planets and stars are destroyed when they strike one another.
They are creatures made of pure energy, or 'souls' as we have named them. The archangels were all 'born' when certain types of energy and elements mingled together. Angels, for the most part, are made from energy gathered from the universe. For example, some angels contain dust from a comet, or winds from the storm on Jupiter. It's said Lucifer and Michael were made from the first solar flares.
Anything and everything. They just watch humanity grow, discover, peak, and destroy itself. Supposedly, what we imagine as the "apocalypse" has happened more than once. Angels are the only things that have survived since the Earth was first created.
Wait, if humans can't look at angels, they why is that one shaped like a human?
A few, rare humans, called the Awakened by those who have knowledge about the Supernatural, can perceive a form for angels. Where, normally, the image of an angel would essentially cause a normal human to spontaneously combust, the Awakened can create kind of a mental form for angels that doesn't overload their minds. Because our minds naturally make up this human-like creature with wings when we think of angels, Awakened can project that onto the formless masses of energy that these creatures are. This allows their minds to better cope with the raw power that's presented to them.
They don't look like anything. They're pure, raw energy that is in a continuous state of motion. They also don't have wings. We just imagine them like that.
When Awakened view them in their humanoid-forms, their 'skin' is translucent so you can see the energy flowing underneath it. The energy can change color. It works kind of like a mood ring, since angels technically can't communicate with humans; Awakened or not.
What reasons would an angel have to make themselves visible to human eyes, anyway?
Mostly they don't have reasons. Some angels just get curious and step out of their realm to be closer to ours. In earlier times, when humanity was new and angels were, too, angels would frequently try to make contact with with humans. This, of course, ended about as well as you would think.
Other times, though, they act upon "God's Will," which means they have to make contact with certain people. During these times, angels will grab a hold onto a vessel, inhabit it, and then complete their mission. They don't stick around in their meatsuit long after that.
Possessions imply there is something still left in the body they inhabit. Only demons possess humans. Angels inhabit corpses or dying bodies. Because of an angel's power, if they tried to possess a body with a soul still inside of it, they would automatically burn the soul out.
Angels prefer to take on bodies with nothing inhabiting it so it doesn't leave behind a premature corpse. When they are finished using the body they've picked up, they usually return it to the grave which they found it in, or place it somewhere that's not extremely conspicuous.
The purpose of a vessel is to allow angels to speak with humans. Angels don't technically speak themselves, and even if they did, they wouldn't speak in any language a human could understand. Not to mention their voices might break through several dimensions of sound.
One more thing about vessels: what happens to the body during and after?
During an angel's habitation of an empty body, the body is essentially invincible. If the body is taken during stages of decomposition, angels tend to clean it up to look presentable to the world around them. It used to be that they would simply just drag the body from the ground and carry out their business.
Well, it's hard to get people to listen to you when you look like an undead creature ready to kill something.
If a limb is somehow detached from the body, an angel will simply reattach it. If the body is punctured in a way that would normally kill it, an angel will just heal over the wounds. The bodies do not need food, air, or water to survive. After the angel is done with the body, it will continue to decay like a body normally would.
You said angels don't technically speak. So how do they communicate with each other?
Angels are basically hive-minded creatures. They have thoughts, experience sensations and emotions (somewhat). When one angel thinks something, all the others know it. When one angel feels something, all the other angels do, too, and etc.
This only ceases when an angel takes on a vessel. This blocks them off from the rest of the Host, which none of them really like. This is why no angel voluntarily stays in a body for long periods of time unless they, for some reason, are trying to cut themselves out of the Host.
What happens if an angel gets caught in a body for too long?
First off, when an angel enters a human body, they are immediately cut off from the Host. They can't hear or feel what any of the other angels are experiencing. Most angels will feel a sense of loss and confusion, making them eager to finish what they need to do in order to return to the Host. There have been a few instances where an angel has either stayed in a body purposefully for a long period of time or gotten stuck by accident.
When an angel is in a human body for long periods of time, the angel starts to forget itself and the Host. Sometimes, it will gain residual memories from the body it habits. If the angel cannot return to its original form, eventually it completely forgets what it is and everything it has experienced. It will walk the Earth as a human, although its power will still be intact. This power, usually, cannot be summoned up and it lies dormant, basically keeping the body going for the rest of eternity. Sometimes, though, the power leaks through, allowing the human body the angel owns to perform great acts of physical strength and healing.
At this point, the only thing that can pull the angel from the body is another angel or completely destroying the mortal coil the angel is caged in. Most angels who are stuck and forget themselves eventually destroy their bodies by their own hands, confused as to why they don't die like everyone else around them and having to grieve for years and years as their loved ones' souls go to rest.
Some angels, ones who cut themselves off from the Host purposefully, have managed to keep their memories intact. They live on the Earth peacefully, for the most part, passing from one millenia to the next without a care.
The big story behind this is covered in the history section, but the short of it is, there was a disagreement among the angels a long time ago. Those who follow Judaism and Christianity knows this as "Lucifer's Fall." That whole story was blown out of proportion, but Lucifer is no longer part of the Host. Some angels who agreed with Lucifer are also no longer part of the Host.
It's rumored they still live on Earth, blending into society around them.
What about fallen angels? Are other angels violent towards the ones cut out from the Host?
For the most part, angels don't care if their brothers choose to live like humans. They feel loss when an angel cuts itself out of the Host, but there are many more of them, so the loss isn't a giant, gaping wound. It's more like a scratch that stings for a while. They also don't seek out these angels to drag them back to Heaven, mostly because it would end in a fight, which almost all angels will avoid against their own kind.
While some angels who live as humans, called the nephilim, did so because Lucifer did first, other angels became nephilim simply because they liked humanity too much. They were awe-struck by humans and their way of life, so they chose to live amongst them and help when they could. Because it's much harder to get their power to leak through a vessel, nephilim have to live by human law and human standards: meaning they can't just do anything they want on Earth.
Here's the obvious question: how much did humans get right about angels?
So, if none of that is right, then what are angels?
They are creatures made of pure energy, or 'souls' as we have named them. The archangels were all 'born' when certain types of energy and elements mingled together. Angels, for the most part, are made from energy gathered from the universe. For example, some angels contain dust from a comet, or winds from the storm on Jupiter. It's said Lucifer and Michael were made from the first solar flares.
What exactly are angels observing?
Wait, if humans can't look at angels, they why is that one shaped like a human?
Okay, then what do angels really look like?
When Awakened view them in their humanoid-forms, their 'skin' is translucent so you can see the energy flowing underneath it. The energy can change color. It works kind of like a mood ring, since angels technically can't communicate with humans; Awakened or not.
What reasons would an angel have to make themselves visible to human eyes, anyway?
Other times, though, they act upon "God's Will," which means they have to make contact with certain people. During these times, angels will grab a hold onto a vessel, inhabit it, and then complete their mission. They don't stick around in their meatsuit long after that.
Vessels? Like a possession?
Angels prefer to take on bodies with nothing inhabiting it so it doesn't leave behind a premature corpse. When they are finished using the body they've picked up, they usually return it to the grave which they found it in, or place it somewhere that's not extremely conspicuous.
The purpose of a vessel is to allow angels to speak with humans. Angels don't technically speak themselves, and even if they did, they wouldn't speak in any language a human could understand. Not to mention their voices might break through several dimensions of sound.
One more thing about vessels: what happens to the body during and after?
Well, it's hard to get people to listen to you when you look like an undead creature ready to kill something.
If a limb is somehow detached from the body, an angel will simply reattach it. If the body is punctured in a way that would normally kill it, an angel will just heal over the wounds. The bodies do not need food, air, or water to survive. After the angel is done with the body, it will continue to decay like a body normally would.
You said angels don't technically speak. So how do they communicate with each other?
This only ceases when an angel takes on a vessel. This blocks them off from the rest of the Host, which none of them really like. This is why no angel voluntarily stays in a body for long periods of time unless they, for some reason, are trying to cut themselves out of the Host.
What happens if an angel gets caught in a body for too long?
When an angel is in a human body for long periods of time, the angel starts to forget itself and the Host. Sometimes, it will gain residual memories from the body it habits. If the angel cannot return to its original form, eventually it completely forgets what it is and everything it has experienced. It will walk the Earth as a human, although its power will still be intact. This power, usually, cannot be summoned up and it lies dormant, basically keeping the body going for the rest of eternity. Sometimes, though, the power leaks through, allowing the human body the angel owns to perform great acts of physical strength and healing.
At this point, the only thing that can pull the angel from the body is another angel or completely destroying the mortal coil the angel is caged in. Most angels who are stuck and forget themselves eventually destroy their bodies by their own hands, confused as to why they don't die like everyone else around them and having to grieve for years and years as their loved ones' souls go to rest.
Some angels, ones who cut themselves off from the Host purposefully, have managed to keep their memories intact. They live on the Earth peacefully, for the most part, passing from one millenia to the next without a care.
Why would an angel choose to live like that?
It's rumored they still live on Earth, blending into society around them.
What about fallen angels? Are other angels violent towards the ones cut out from the Host?
While some angels who live as humans, called the nephilim, did so because Lucifer did first, other angels became nephilim simply because they liked humanity too much. They were awe-struck by humans and their way of life, so they chose to live amongst them and help when they could. Because it's much harder to get their power to leak through a vessel, nephilim have to live by human law and human standards: meaning they can't just do anything they want on Earth.