So this guy I like ( we are just friends, NOT dating, but he knows I like him) is giving weird mixed signals and keeps on acting hot/cold. I believe he's a little (alot) shy... (yes or he could be completely disinterested... ) but my question here is:
How have people dealt with shy guys in the past? How do you know if someone shy is interested but is just nervous? What is the best way of dealing with him?

Well... you could just let this go on forever... and if he's as shy as you say he is, then this'll go on until you lose interest. Or, he could potentially make a move.

If you want something done, you got to do it yourself. Want to date him, then ask him out for a movie.

Sometimes you can tell from their body language that they are shy, they maybe a bit fidgety or shaky and may avoid eye contact. If you want to know and can't detect from his body language, you can always ask him out like ISneezeFunny said or ask him if he likes you or what he thinks of you for a direct response. Good luck!

If you're interested in HIM, his shyness shouldn't matter. Just let him know in a calm, unpressured way you'd love to do something with him sometime if he's ever interested. He can give you a call and hand him your number on a card.

If he calls, great. If he doesn't, don't freak out. He has to choose. Let him choose. You've rolled out the red carpet at this point, if he doesn't walk down it, not much more can be done.

Yes! You're right... I've done enough, he has to be the one who takes it from here. And if he can't do that for whatever reason, then I move on.
(always easier said than done)

Just from experience,I'm kind of shy when it comes to people I like. Just talk to him about it, what he feels and stuff. What do you have to loose. Else you will always think "what if" It worked for me. Just talk to him about it. It may be hard but...

I'm not sure how to bring it up or if I should. We started talking about it before, and he kind of freaked out, and he's been weird since then. He's been kind of avoiding me (though he still calls me sometimes), so that's why I don't know what to think.