Take the light squares and lay them face down, so you're looking at the wrong side of the fabric. Use a pencil or quilt-marking pen and draw a diagonal line down the center of the block.
Lay the dark and light squares right sides together, with the light fabric on top so you're looking at the diagonal line you drew.
Sew, using a 1/4" seam allowance, a straight line down each side of the diagonal line you drew.
Cut the blocks apart on the line that you drew
Press your HSTs
Line the block up so you can "square it up" or trim, as some people call it, to whatever size your HST needs to be. Mine need to be 3.5"
Now we have 2 finished HSTs, size 3.5". This is the size you need to make a 9" finished block. I was making churn dash blocks and simple friendship star blocks when I did this tutorial.