In case it is easier for you to read how to do it I will just write it here.
1) Start a regular french braid, either before or after your bangs.
2) Once you get to the side of your head start the waterfall by splitting the bottom chunk, dropping most of it, and adding in a new chunk with what is left. Or just drop it and grab a new chunk.
3) Continue to add in hair on the top side like a normal french braid and continue splitting/dropping the bottom piece replacing it with a new chunk.
4) Get bigger pieces as you go.
5) End it by putting a small rubber band near the top of the braid and let the ends fall just like the rest of the waterfall pieces or continue it until you have taken all the hair around the top of your head.
6) Do a normal braid to end it and then use a rubber band.