This is a series of 3 pictures, showing the assembly of the base supports. It took me a few minutes to figure out exactly what they wanted you to do so I thought I would save someone a little time by showing you what I finally figured out.

The first picture shows support pieces D on the left and E on the right, apart from each other. Support piece E has support piece B inserted at the end.

The second picture show support piece D on top of support E and B.

The third picture show how you then slide support piece D down to connect all three pieces together. Support piece D has a slot in it so you are able to slide it down.