Download the latest version of iTunes if you do not already have it on your computer. Decide which music files you want to transfer from your computer to iPhone. If the files are not already stored in your iTunes music folder, move the files into iTunes. Right-click the files and select Open in iTunes. Alternatively, you can drag the files from the original folder location into the iTunes interface.
Using the USB cable provided with your iPhone, connect your iPhone to your computer. If iTunes is not already open, it automatically opens. An icon of your iPhone appears in iTunes. If your iPhone icon doesn't appear, click View and then Hide Sidebar.
Click on the icon of your iPhone. It is located in the upper-right corner of iTunes. Click the Music tab. Complete the file transfer by clicking the Apply button in the lower-right corner of iTunes. The music in your iTunes library is transferred to your iPhone.