The figure-of-eight is used mostly as a stopper knot, similar to the overhand. It is a little bulkier, so does a slightly better job in this regard.
If you can tie one of these, then you should also be able to tie the figure-of-eight on a bight, which is a very useful knot. It is also the starting point of the rethreaded figure-of-eight, so is important to know for that.
Note that in very flexible or thinner diameter rope, the knot will set slightly differently.
|Pass the end of the rope over itself...|
|...and then back under itself.|
|Feed the end of the rope down through the loop formed.|
|Pull tight and set. Note the distinctive shape of the knot.|