If you tap on the 4 horizontal lines icon beside the text box, you will see a list of commonly used texts (e.g. D.C. al Coda, D.S. al Coda, repeat times) that are also understood and interpreted by the Player.

You can add any text, simply type in the text field at the current cursor position.

The two arrows will allow you to move the text up or down.

Some users have found ways to add lyrics using the text in the editor.

See their solution here.