The Apple iPhone has an iTunes application that enables you to purchase music directly from the iTunes store, then downloads it to your iPhone's music library. In order to keep your iPhone and your iTunes program synchronised, it is necessary to periodically transfer the music to your computer. Synchronisation not only keeps both devices up to date, it also creates a copy of the file in case either device experiences data loss.
Click "Start," "All Programs," "Apple" and "iTunes" to open iTunes on your PC. For Macintosh computers, click the "iTunes" icon on your screen's dock.
Click "Tools" at the top of the menu and click "Authorize Computer." Type the email address used by your iTunes account and the password, then click "Authorize."
Plug the USB cable into the iPhone dock connector and plug the other end into the computer's USB port.
Click "File" at the top of the menu and select "Transfer Purchased from iPhone" from the drop-down menu.