To make an ordinary fishtail bracelet, you would simply continue this step until the bracelet was long enough. For the inverted fishtail, this step is just to make sure all the rubber bands are secure before you begin the trickier inverted pattern.
This stitch is very similar to the regular fishtail. The only difference is that the bottom band comes up inside the middle band and then outside and over the top band, rather than going outside and over both of them.