How will braces fix gaps?

Last Wednesday I got four of my bicuspids pulled (and wisdom teeth but that's irrelevant) due to crowding in my front teeth. I'm getting my braces on next Tuesday. I was just wondering what kind of tools my orthodontist will use to fix the giant gaps from the extractions. My friend said they put a spring there but I've never heard of it before. Also, I'm still trying to decide what color to get. Any ideas?