Hi, I have played guitar for almost 2 years. I've learned most from tabs, playing songs of my favorite bands and stuff like that..

I have been on the net and tried to learn some theory. I wrote down some scales, like the blues, major, minor, pentatonic... and I read some tutorials about a lot of stuff but....
the reason i wanted to learn it was because when im sitting and trying to come up with rifs/songs i hit a dead end u know... not much comes out, very rarely....
it feels like im sitting there just playing random on some strings u know.. oh btw yes i know the notes on the fretboard/strings etc.

If you look at bands like Metallica, Pantera, Iron Maiden, Slayer, Megadeth etc...
What do they need to know, before making those songs?
Not how they full off the solos, I want to know more like riffs/rhythms n stuff like that, but also some melodies for sure.

I would appreciate if someone could write some stuff I could practice and put into my "songwriting" process when I'm messin' around.. And maybe give some examples from places where these mentioned bands used "balbal" in riff xxxx for example.
I know that dimebag used the blues scale for cowboys riff for example :p

riffs etc, u write it from scales?

how to use scales effectively in songwriting (not solos)?
what is chord progressions and stuff like that?
what do i.e. James Hetfield need to know as the rhythm/composer in Metallica?

I'm really frustrated since I never get any good answers >.<
I deeply appreciate comments by anyone who think they might help me!

Thanks and Bye!
Writing it by scales is useful.
But what's also very useful, for me, is just playing with some friends and exchanging riffs or small parts of songs together.
This is the way we did it and it worked out very nice.
Check our songs.
All without scales.
Just did it for fun.
Try it, might work fro you also
You don't have to hold the door open for me
I can do that myself
I might want to make some song texts for you if you give me an idea of how you play.
What kind of music do you play and can you do hammer-ons etc easily.
You don't have to hold the door open for me
I can do that myself