I think you might mean half square triangle. You put two fabrics rst. Draw a line from corner to corner, stitch a quarter inch each side of it, then cut on the line. I press then square up with a square-up tool. The other tool you can get is a half inch ruler marked in center, you line it up and marke the two seam lines. Sew on them and cut between. You can also buy paper templates for this method. The square up tool i use is a square ruler with the diagonal line marked and square sizes marked in quarter inch increments. I hope this helps you.