Every one needs to know their knots.
Wether your a sailor or a hiker or just the random person, you are going to come across knots EVERYWHERE.
Now knowing that is one thing but knowing Them is another! Learn your knots, they can save you allot a hassle. Think about it, if you can tie one knot that'll slip in a week or even day so you have to re-do it or tie a knot that'll last you week/months or years, what would you choose?
Here is a site with animated help that is easy to learn from with no hands in the way:
This site has allot so if you need a knot for sailing or anything, so they sorted them in categories.