Story of Slender

I'm new here. I got into Slenderman from people talking about him at school, I looked into him, downloaded the game and came here. I've heard stories about him but I don't agree with their stories because they are just silly (And wrong) so can  anyone tell me the story behind Slenderman. Not how he was created, I know that much, I want to know what he does, where he goes, What he can cause, When does he attack, what is the story behind him, etc.
What, When, Where, Why, How, But I know who

What I know so far:
1. Kidnaps/kills Humans
2. Tall and long
3. Teleports
4. Causes Photographic and Video distortions (static)
5. Tentacles on his back
6. No face dressed in a black suit, white shirt, and red tie.
Tell me more, or correct me if I'm wrong (I may have forgotten some other details).

Eh...I'm not so sure I can give you one answer, as it varies from series to series. Sometimes he is portrayed as a god, sometimes as a human test subject gone horrible, etc.  

He has different abilities per series too. In some he makes people go insane, in others he can cause physical harm, and in some he has proxies do his work. Sometimes he can warp time as well as space, and sometimes he is just a paranormal being, and that is all. Sometimes he has allies, sometimes he has enemies, sometimes he works alone.  It is really dependent on the series.

The Slender Man's abilities and origins are allways portrayed inconsistently because he is supposed to be up for interpretation, but this is a decent list of abilities he is often portrayed with.

Thank you Peppercorn this really REALLY helped. Thank you very much.
Now all I need is his story, and Where Knifeman was going with it is what I want. So if there is as you say a lot of stories behind him, maybe tell me your favourite or the most juicy of them all. And I preferably like creepy ones, I mean if you like Slender you like creepy.

Hm...Well some particularly interesting "life stories," (I guess you could call them) about him are the ones in TribeTwelve, where he runs a group of God-demons, TheRiddleOfTheTreeman, where he is a physical nightmare of a God sent to terrorize humans, DarkHarvest00, where he is worshiped by a cult, and was brought to earth by a scientific experiment, and EveryManHybrid where he works with the Rake and a being called HABIT to slowly kill and destroy the live of the main characters, who happen to be iterations of themselves (this basically means that if all of them die, they "respawn," in a decade or so and the cycle continues).  

I suggest checking these series out, and for TheRiddleOfTheTreeman, I'd follow the trailhead here and at unfiction to understand it. For EMH I'd use either the Timeline wiki, or this channel:

 https://www.youtube.com/user/NathanCHaskew?feature=watch

Which has all seasons uploaded (except for the fourth, which is in his playlist for the series).