This 2 minute YouTube video shows a man demonstrating how to tie a basic square knot. He explains that the square knot is useful for tying two ropes together of similar thickness. The man holds up both ends of the ropes and ties an overhand knot in one, then passes the working end of that rope through the loop and pulls it tight to complete the square knot.

1. http://www.youtube.com/watch?v=ee6MnJ7iL2s