We did this on triangle day for preschool.

Start by parting the hair from one ear to the other.

From the front to the line in the back, make a triangle. Like so.

When I originally did this, it was a lot more polished, but you get the basic idea. You now part from that first triangle, another triangle. Like so.

Repeat until you reach the ears.
Now, here is where it is up to you. I parted my middle triangle into two and pulled the ponytails from each side into one ponytail. You could do two ponytails with all of the hair...whatever.

Now, after I did that, I realized that the ponytails were a little droopy and that made me sad.
I don't like droopy.
So I pulled the two ponytails into one ponytail. And I made my triangles into a square.