Imagine you are at a point A and you want to go to a point B. You must travel in the direction that takes you from point A to point B. You can plot the positions of A and B, and find the bearing from A to B by superimposing on A a compass, with angles labelled from 0 to 360 degrees.

We can then just read off the bearing from A to B.
If A and B are given as position vectors
 and
and then it is useful to find the vector
then it is useful to find the vector and plot it, on a compass with the centre of the compass acting as A.
and plot it, on a compass with the centre of the compass acting as A.
The bearing will be given by
 if
if and
and are both positive
are both positive

 if
if is negative and
is negative and is positive
 is positive

 if
if and
and are both negative
are both negative

 if
if is positive and
is positive and is negative
is negative
