I am so bad with computerstuff. Just "marked" the T - shaped piece of fabric. You have to make a little cut in the corner where the middle marking is and sew together to the other two markings. There you make again a little cut into the seamallowance of the long piece of the t- shape and close the rest. Do the same thing on the other side. Hope this helps, you might want to try with a piece of paper the get a t- shape into a box.