Yo man,
if you're into rock and stuff then instead of reading tutorials and watching youtube videos you should be out somewhere... screaming.
That's the point and that's the problem - people are always searching for a way to do stuff when it's enough to just do it instead.
My advice (I'm a crappy rock/metal singer myself) is that you should absolutely let go and practice a little singing-buddhism. It's funny but actually it works: clear your mind and stop being yourself for a while, let go all the worries that somebody might hear you etc., when you're worried - you'd never ever ever scream well.
Then you just gotta scream your lungs out through the mouth and in time you'd just get to it yourself - by practice, not by reading. In time you'd find ways to scream in exactly the manner you want and can without damaging your voice (or maybe a little, but to hell with this, yea?).
I remember myself that at first I was losing my voice after five minutes, a week ago I've done a 1,5 hour punk-rock rehearsal and felt that I could scream for another hour
Just scream!
Hello everybody, I guess that's a good first post