To light a mode you need to fill up the hit targets P-O-T-T-E-R, which are purple. You will start the game with half of them lit for your first mode. For subsequent mode starts you will need to light them all.
To start a mode (once lit) hit the right kicker which will be lit purple when ready.
The mode that will start is based on which light is lit on the playfield. These lights move right to left with each hit to the slings.
Pro-Tip: You can bring modes into multiballs, and it’s a great way to stack your points.