The song editor
The song editor has a list of all songs in the project. You can add a new song by clicking the plus button at the top of the list. You can delete a song by sliding it to the left and hit the delete button or by clicking the minus button at the top of the list. If the project is shared on a file sharing service this requires the lock on the song.
The selected song is shown in the editor on the right side. The editor has several tabs for different parts of the song: