With the iTunes software program, you can play back the songs in your audio collection, download new songs and organize your audio files into playlists. Apple mobile devices, including iPods, iPhones and iPads, use iTunes to update core software and sync audio across devices, among other tasks. The check boxes next to each file in iTunes control a song's playback and syncing mode.
Effect on Syncing
After you set iTunes to automatically sync with an external Apple device when you plug in such a device, iTunes will move any new music files onto your device automatically if that song's check box is checked. Remove the check in the check box, and the song will remain on your computer, but will not transfer to your mobile device.
Effect on Playback
When you deselect the check box next to a particular song, iTunes will not automatically play that song in a given playlist or when you play your entire library; instead, it will skip over it. You can still play the song individually by double-clicking it.
Remove a Check
To deselect a check box, click the check mark once. The check mark disappears, leaving a blank box. Hold down "Cmd" on a Mac or "Ctrl" on a PC while clicking to deselect an entire list of songs.
Restore a Check
To restore a check mark so a song once again syncs to your Apple mobile device and plays in a given playlist, click the empty square once. The check mark symbol reappears. Check all the songs in a list by holding "Command" on an Apple computer or "Ctrl" on a Windows computer while clicking a single box in the list.