You cut 2 pieces of fabric, one an inch or two larger than the other. Doesn't seem to matter much about sizes, just do them all the same.
Sew fronts together with pleats in the middle of each side,leave an opening to turn it. Stuff it to your desired fullness and hand sew the opening closed. Then sew it to the others.
This is a good take-along project to work on.
I think one of my daughters has one I made at night while she was small, while my ex-DH was stationed TDY overseas.