To being....lay out your pieces
Line up the first triangle matching the corner of the square with the corner of the triangle
Stitch using the normal 1/4" quilting seam allowance
Line up the second triangle matching the corner of the square with the corner of the triangle. Where the triangle points extend, this should measure 1/4".
Press to complete the triangle corner unit and trim tail.
To stitch this unit to a square, finger press the square to establish the center
Pin through the intersection of the triangle unit matching the finger pressed center of the square. Sew directly through the intersection. Doing so will ensure you do not cut off the corner point.
Repeat the same process on the opposite side of the square and press. Add the 2 remaining triangle corner units to complete the block.