How to transfer music from my computer's hard drive to my iPhone 4S?

How do I transfer music from my computer's hard drive to my iPhone 4S?

ITunes ***

For iPods you need iTunes. I'm guessing it's the same for the iPhone.

You have to play or install the music on iTunes, then go to the iPhone Music tab (at iTunes) and choose which songs/playlists you want to be synced.

Just add all your music (mp3, etc) into the itunes list, then sync to the phone.