Tying knots is an essential part of sailing. Most boats have plenty of rope, as rope is the most effective form of running rigging. Today I won’t go into the details of knot tying, but rather I will refer you to simply the best website there is on knot tying.
There is no need to buy a book any more with resources like this, in fact I always found learning from static pictures rather difficult. Animated knots gives you clear visual guides to tying knots.
If you are a dinghy sailor, you can actually get away with just two knots. The figure of eight and the bowline. If you are sailing a bigger boat there are probably 3 or so more knots that come in handy.
Nothing beats practice, and the ability to tie a bowline on a bouncy boat, in the dark, is a definite bonus skill. So get that bit or rope and keep on practicing.
The site to visit is
Animated Boating Knots by Grog
Enjoy it, it is good.