Frostwire is a p2p software build up on the popular Limewire code. It is completely free and open source. Teens usually use this to download tons of music because it literally has got millions of mp3 files available. If you are looking for some specific music, there is a high chance that you will find it in there.
But be careful before you jump into using the Frostwire. You do not want to burn your hand in all the excitement. This article, Is Frostwire Safe. is Frostwire Legal. Frostwire Review will put everything in perspective. Remember that Frostwire is not the only option for music download. There is Ares. Here is a good article on Ares. Is Ares Safe : Ares Music Download. Ares Review.
Having a p2p software is like having a Gun. You can legally own a gun but it can be illegal if you do not use the gun wisely. Keep that in mind while using any P2P software which claims to be the best source to download free music, software and documents.