Here you get a look at two half hitches. That is really a clove hitch on the standing part (the long part of the line). Then a rolling hitch thrown in.
Laser sailors sometimes show up and don't have the knots down. There is not much knotting, but you do need to know:
Two half hitches
Bowline (this one takes practice till you know it.)
Go to "Animated knots by Grog.com" Do the boating group and learn the above knots.
If it is too windy or too calm, then practice your knots or help someone else.