Download and install iTunes on your computer, after that allow iTunes to have access to your music file then you can connect your iPhone to your computer and open iTunes, in the left panel in iTunes you will see your iPhone icon, clic on that icon and you will see a new page in iTunes with your iPhone informations, on top of that information page, there are some tabs, you will see contacts amount those tabs, select music tab and check "sync" then down left conner of that page, you will see another "sync" icon, click on it and iTunes will sync your musics to your iPhone.