I spotted this boat at Blakeney in Norfolk! What happens if you want to go north but the wind is blowing north west? You use the idea that the wind is made up of one part north and one part west. You angle the sail to catch the north part. We use this idea a lot in Physics. It isd called RESOLVING FORCES and two parts (north and west here) are called COMPONENTS. Notice that they have to be at 90 degrees to each other.