Need help learning how to square fabric for roman shades. i don't have a clue about using t squares.
By squaring fabric I assume that you mean evening out the ends. I usually go about half inch from the edge and take a thread from the fabric and pull it all the way across. The uneven part will come off and you will have a squared end.
Another way is to tear it. The following site might help.
Here is a link that might be useful: Squaring Fabric