This is a bit late but I only ran across your question this afternoon.
It needs a particular shape of T, made of five connected squares. There are three squares across the top and two further ones below the central square, forming the upright. To actually do it, you'd have to cut one out of paper or cardboard. But you can see how it works with a rough drawing.
The first cut is from the outside top corner of the crossbar through the junction where the upright meets the cross-piece and out through the other side of the upright. You now have your first triangle, half a square in area, and two odd-shaped pieces. Stack the bottom part of the upright on top of the cross-piece, square ends flush. Cut in line with the edge of the upright so two squares fall off the end. In your hands you will hold two more triangles, of half-a-square and two squares in area.