So I'm going to start off by saying I'm 16, so I don't know much about detecting what went wrong with my car.

I drive a 1999 Acura 3.2 TL, and I got in it this morning to go to school. When I started my car, everything seemed fine, but after a few seconds of idling I realized something was wrong. The engine dropped from its idling RPMs of 1K to 500, and a belt was squeeling. Then my car went back up to 1K RPMs and all seemed fine, until it dropped back down to 500 RPMs and did the same thing, so I turned the car off. I got my mom and had her start the car so I could look under the hood. I couldn't see anything wrong, but I could tell that the belt that was squeeling was the main belt right next to the engine. My question to all of you is can you tell me what's wrong with my car?

UPDATE: So it is the AC Compressor, a thousand thanks to everyone who helped.