Can I download Music from my PC's Itune Library to I-Phone 5?

Just connect the iPhone to your PCs USB port, select the iPhone from the Devices list in the left sidebar, and if you want to selctively transfer music, choose manual sync in the main Summary window. Then check the music to sync and click sync. Or to sync all of it, do not choose manual and just select sync.

When you finish you have to eject the iPhone.