It is a simple Compass app which uses magnetic field sensor.
so you need a smart phone with built in magnetic sensor.
Smart phone compass in your pocket!
Mountaineering , orienteering , military, You can use this app anywhere.
* How to Use:
1. Hold your smart phone flat.
2. turn your phone horizontally as the arrow overlaps the red double parallel lines.
and check the red edge of the arrow point zero degree(0'N) otherwise the red edge could point south,
then red edge points north, right side points east, left side points west and down side points south.

Note:
Some phones will give different sensor readings based on the hardware used by the manufacturer.
And If there are magnets or electronics around, It will show inaccurate result.