The Judo belt (obi) is wrapped twice around the body with the center of the belt just below the navel. Then a knot is tied in front as shown in the videos  below. The ends should be of equal length at the front when you are finished.

Ashley McKenzie – How to Tie a Judo Belt | Sport Relief 2014

How to tie your judo belt

If you are still struggling here is another video worth looking at:

A Different Way to Tie a Judo Belt

In this video we see a different way to tie a Judo belt, this might be a little advanced for some but it is worth a look.