The light-up letters are battery operated.  The On-Button(s) are accessible from the back of the letter - be aware some letters have 2 sets of lights.  You can push the button(s) by going through the small hole(s) in the back of the letters.
 

The lights have 8 settings you can cycle through: 

• 1- Combination

• 2 - Wave

• 3 - Sequential

• 4 - Slow  Glow

• 5 - Chasing Flash

• 6 - Slow Fade

• 7 - Twinkle Fade

• 8 - Steady on

• 9 - Off

The lights are on an Auto Timer, they will shut off after 6 hours.  They can be easily turned on again by pressing the button again.