Android :: Show The Direction On Screen That Phone Is Facing

I want to show the direction on the screen that phone is facing.

For example:

0
|- []
|_
South --- North

In the above diagram the phone would display "North". Since the user (the stick with 0 for his head) is holding out the phone (the [] in the diagram) pointing north.

I found this example. I understand what it's doing except it seems to calculate yaw, pitch, roll, and inclination. What are those and how would I use them to simply find which way the phone is pointing?

Also this android documentation mentions X, Y, and Z axises but I don't see anywhere that says how those axises correspond to the phone? Is Z going from the bottom of the phone to the top?