A secure Cleat Hitch is necessary when tying up to a dock.
Another good knot to know.
A bowline is one of the most frequently used knots. Watch this video to learn how to tie one.
Round turn and two half hitches is also a very strong knot.
Keeping your lines neatly coiled is very important on a sailboat. Why? Because if a line falls in the water, it might wrap around the prop and sink the boat. Not a good thing.