So when you write a song, its basically a bunch of riffs right? how do you know which riffs fit together? do they have to be in the same key? how do you find out what key a riff is in? how do you write a follow up to the intro? if you can answer any or all of these questions that would be cool.
Hey champ, since your questions are music based, and it doesn't sound like you know much music theory, I'd recommend this book I'm reading right now, "The Complete Idiots Guide to Music Theory" by Michael Miller. It's very good, and once you have look at this book all of your problems will be solved.