Definition :

This is the thing that you steer the yacht with, on the yacht we will have it will look like a big wheel, Turn it to PORT (the left) and if the yacht is going forward, the BOW (Sharp Pointy End) of the yacht will turn to PORT (the left) and the rest of the yacht will follow. Turn it to STARBOARD (the right) and the whole thing will happen to STARBOARD (the right).

Now for some reason that could be explained with a lot of diagrams and other boring stuff, things are quite different if you are going ASTERN (Backwards). Leaving you with that confusing thought, here are some pictures depicting the Helm and some people operating it.