In the editor, if you're on the Slides tab, you can double click in the text box on the slide on the right to be able to type text. 

If nothing is showing in the slide when you enter text in the Words tab, go to Inspector and click on Slide and make sure the Song box is checked. If it isn't checked, then that means the song text box is turned off. If it's doing this to all your songs, then it might be set up that way in your theme. Edit your default theme and turn that text box back on and save it or change your default theme to something else.