It may be easier for you to try it with a pendulum (just a weighted object on a string, don't have to buy one necessarily). You shouldn't expect the board to rearrange itself or anything dramatic like that.

What you're trying to do is to open up your subconscious and allow any communication to come through the unconscious/unintentional movement of your muscles. You should find that this is easier with a pendulum than a finger, because the pendulum can pick up smaller movements. So what you would want to do is allow your pendulum or finger to move over the board and point to different letters without you intentionally or consciously moving it yourself. Hopefully these letters will then spell out words and sentences. The tricky part is really just stepping back and preventing your conscious mind from influencing the results.

You may find these topics to be of interest:

Pendulum Any One? (Link)
So how accurate are pendulums? (Link)