This article is for new iPhone users.
At some point you’re going to want to put music one your iPhone to listen to. You can do this without having to buy music from the iTunes store, if you have music available on CDs or in MP3 files.
What you do is install iTunes software (downloaded from Apple.com) on your desktop computer. Then you import the music into iTunes from CDs or MP3 files you have. After this, you plug your iPhone into that computer and use iTunes to transfer music to the iPhone.
You only want to do this from your own desktop computer which you plan on using in the foreseeable future. This is because Apple tries to enforce content protection by designing the iTunes software only allow content from one machine at a time. So if you go to a friends house and want their music on your iPhone, the iTunes software on their computer will clear all your songs and content from your iPhone before letting you transfer music from their computer to your iPhone.
This is why you want to use iTunes on your own personal computer to import music, movies, and other content to your iPhone. Also, when you sync up, information from your iPhone is also backed up to your desktop computer. So if your phone is ever lost or stolen, you can bring all the information back into a replacement iPhone.