http://www.gcseguide.co.uk/bearin2.gif

Bearings are used to describe an angle with respect to some other known direction.

Let's say two ships are navigating in the middle of the ocean on a foggy night. The fog breaks for a second and one captain spots the other's lights only a mile away directly in front of him. Then the fog rolls back in, and they're blind again. Afraid that they might collide, the one captain hails the other on the radio and asks "What direction are you going?"

That captain replies, "Straight ahead. How about you?"

Obviously after that short conversation, the first captain still has no clue whether they're going to collide or not. The only way to know for sure is for the other captain to specify his direction of travel with respect to some KNOWN direction. For example, if he'd said "I'm heading 15 degrees west of north," the first captain would then be able to determine with certainty, based on his own heading, if he had to change course to avoid a collision.

Bearings are a way of providing a consistent reference so that directions can be specified with certainty.