I've just learned how to do this braid and it's already one of my favorites.
First, gather all the hair up into a tight ponytail. Once it's in the elastic, section it out into five equal pieces. This is where it gets a bit tricky... Start with the outside section on one side and take it under the adjacent section and over the following section. That outside piece should now be right in the middle. Grab the outside section from the opposite side and do the same thing - under the adjacent piece and over the next piece until that section is in the middle. Continue this down the entire braid, rotating from right side to left side. I know that probably sounds really confusing and it does take a little practice to get your fingers where you want them. Good luck and it's worth the practice!