Bearings are a measure of direction taken from North in a clockwise direction and the units used are in degrees written as three figures. Therefore when travelling North, the bearing would be 000°.
For example, when travelling from point P in the direction of the arrow in the below image, the bearing would be 085°.
Below is an illustration of the compass points which are used when calculating bearings.
Back bearings is the movement to describe the turning back from an original point. As bearings are always measured in a clockwise direction, they are therefore longer than the original bearing. For example:
If the bearing from point A to point B is 105º, what is the bearing from point B to point A?
From angle B to A is 105º + 180º = 285º