1. Open the Editor.
  2. Tap on "abc" and enter the text you want.
  3. Use // to add second line of text.
  4. Tap on Done to exit the Text Editor.  

In the text editor, if you tap on the 3 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 text field at the current cursor position.
The two arrows will allow you to move the text up or down.

Use the // characters to add a second line of lyrics.

Some users have found ways to add lyrics using the text in the editor. 
See their solution here.