Root key: set this song's root key (at least the key value; click the Minor checkbox to designate it as minor). You can only select from the root keys "native" to the current chord format: for example, if English is the current chording format, you can only select from A-G, not Do-Si or I-VII. If you want to create a song in another chording format, you must change the default format first, or convert the song later.