To “check mark all songs in iTunes” is to select all of the songs in your iTunes library. This can be useful if you want to quickly select all of your songs to perform an action on them, such as deleting them, adding them to a playlist, or burning them to a CD.
There are a few different ways to check mark all songs in iTunes. One way is to use the keyboard shortcut Command+A (on a Mac) or Control+A (on a Windows PC). Another way is to click on the “Edit” menu in the iTunes menu bar and then select “Select All”. You can also check mark all songs by clicking on the first song in your library and then holding down the Shift key while you click on the last song.
