What happened to the music I downloaded onto my iPhone?

I have an iPhone 5s and I used iTunes to download my music.

The sync was complete, but when I clicked on the Music app and went to my library, it showed nothing!

s wrong?
IIm a new iphone user.

You may have hit the sync music check box which changes the way you choose to add songs to your phone. This couldve deleted them

Once you plug your phone in, select your phone in iTunes then go to the music section. From there you select what music you want, by default it doesn't select anything so if you don't select the music then nothing will sync over