I want to knit a teddybear for my girlfriend, how do I go about doing it?

This project would take a mive amount of time, given that you don't know how to knit. Since you know how to crochet (even just a little bit--it's simpler than knitting), why not look up an amigurumi bear pattern? Much easier, much faster, and you'll have a background on the craft to begin with. And they look cool! You could use balled up shopping bags. You could also use old scraps of cloth, torn up tee-shirts, etc.