"I don't quite get the part about not sewing along the weave."
The fabric comes in a roll, 60 inches wide and however long they cut it off for you.
The threads in the fabric go in the "long" direction and in the "wide" direction. If you pull on these it will stretch a little differently. Ideally, if you sew two edges together, they should both be in the "long" direction or in the "wide" direction.
Edges that go at an angle, like the "zipper" or "ground" in my picture above stretch differently. You want to avoid sewing an edge that goes in the "long" or "wide" direction to an edge that goes at an angle. When you set up the tent it won't be as taught. There will be more wrinkles.
In the picture above, the edge labeled "end" goes in the "long" direction and should be sewed to the end triangle piece on an edge that also goes in the "long" direction.