Set it on your bedside table, tap it when you lay down for sleep, and then it will slowly pulse light onto your ceiling. If you match your breathing to the in and out waves of the light brightness you will slowly start to feel more tired. It gives you something to focus on and stay in sync with your breathing. Over the course of 8 or 20 minutes (depending on which you chose) the pulsing will get slower and slower, thus gradually reducing your breathing rate and helping you wind down into sleep.
It works decently well on me, but I've moved on to meditation for sleep and don't use this anymore.