When editing a show, you get a few buttons in the center bottom on of them show a "note" icon. Click on that to enable chords mode. This will show any existing chords, and add a "+" button in the top right corner of all the textboxes. Click that button to add a chord, or you can right click to choose from a list.
All the chords can be dragged around in the text when chords mode is enabled. (This is currently very buggy)
Show chords in stage display
You have to enable the chords in the stage display by selecting either a slide textbox and enabling "Chords" on the right side.