what is gel paint and where would you use it specifically?

Are you sure you don't mean gel stain? If so, it is primarily used for what's called "graining". Personally, I use it on steel doors, but you can use it on any smooth surface to create a faux wood grain. You can actually take a metal door, or any metal surface, and make it look like it's stained wood. With it being a gel, when you brush it on, the brush strokes create hills and valleys in the stain since it is thicker. With a lot of practice, you can actually make it look identical to stained wood.

I know about gel stains and gel varnishes but the only gel paint I know of is for fingernails.