how to download free music to itunes?

Go to the iTunes Store. Tap music at the bottom of the screen. Scroll down to Free on iTunes. Three are only two singles you can download for free right now. You're better off with a music app like Pandora, Jango, TuneIn Radio and iTunes radio amongst others.

Go the iTunes Store and search for free songs. There are some available, but it will take you years to build a decent music library if you expect to get free songs only.