Tying knots is a very important skill for any outdoors-man to have, not just for survivalists but also for Hunting, Fishing, Boating etc.
In the above infographic you will notice that there knots and hitches. Knots hold together without another object, Hitches are knots that use other objects, typically a post, stick or sometimes another knot.
The ability to tie a knot in a survival situation can be very useful. You can use this skill to tie someone to a rope and pull them out of a ravine, tie together a shelter, make a cargo net for a fish net and many more.