Depends on what you mean by "create models". If you want to make something from scratch, you're going to have to do poly-by-poly modelling (if you're working with Milkshape), then you're going to have to unwrap the mesh so that a skin can be applied. I'm not even going into animations, because that would mean you'll have to create a skeleton then animate the bugger frame by frame, which I actually find very fun. But regardless, doing it all without knowing anything starting off is an extremely tedious task.
Not trying to scare you off, it really is just a very complicated process.
Now there is another method you can go with called hacking. Not to be confused with illegal hacking, basically what you will do is decompile a premade model and edit it by changing the mesh or taking parts from other models and combining them. Hacking models isn't generally looked down upon the way decompiling a map is. 9/10 models you find on places like FPS Banana are hacked models.