The MP3 file format has revolutionized the way music is obtained and listened to. From the Napster controversy to pocket-size MP3 players to being able to store an entire music collection using only a few gigabytes of disk space, MP3 has had more effect on music than almost any other innovation (certainly any digital innovation, anyway). iTunes provides all the MP3 tools you need in order to listen to and create your own MP3 music.
Depending on how you got your copy of iTunes, the Library might contain songs already. For example, if you purchased a new Mac that had iTunes installed on it, Apple might have preloaded some music in your Library. You can use or remove these songs as you prefer.