A Half Square Triangle block is made using 2 fabric squares of the same size but different fabrics.
Place the 2 fabrics on top of each other with the right sides together. Draw or mark a diagonal line from corner to corner on the wrong side of one of the fabrics only.
Sew 2 lines parallel to the drawn line, one on each side. Each must be ¼” from the drawn line. After sewing, cut on the drawn line. Press the pairs open with the seam allowance to one side. You will have 2 Half Square Triangle blocks.