How to synchronize music between PC/Mac and your iPhone.
1) Drag and Drop your music file into iTunes Playlist to copy.
2) Connect your iPhone/iPad to PC/Mac, then select "MUSIC" and click "Entire library" in case you want whole music else you should select each.
3) After complete the synchronization, the same Playlist shows up on your iPhone device.
4) In case you have trouble, please check "OFF" on Setting>Music>Sync Library.