ASCAP is a Performing Rights Organization, they are the ones that pay you when your songs get played on the radio, TV, movies, etc. You still have to copyright your music, then after you copyright it you register it with ASCAP and they keep tabs on many spins it gets and the like.
You might make a little bit of money, but the real money doesn't start coming in until you get on the charts or get placement in a movie or TV show or video game or whatever. If you make a #1 single then your check could possibly be upwards of 500+ thousand dollars. Just don't expect much at first. You should still sign up with either them or BMI and register your music with them because there is no telling what can happen.