I've seen a couple examples of these Fundamental Polygons/Planes, but I do not understand how they're derived or what they even mean.
I'm fairly new to the subject in general.
As an example, the Klein Bottle has the fundamental square where two parallel sides point in the same direction, and the two others in opposite directions. I've also seen a version where a circle is used instead. I don't really understand what I'm supposed to get from these representations.