For block 3 you will need:
8) 4" light (background) squares
4) 4" red squares
4) 4" blue squares
Draw a diagonal line on the back of all of the light squares.
Match the four red squares with 4 of the light squares making sure the right sides of the fabric are facing and the outside edges are aligned. Match the four blue squares with the remaining light squares.
Sew 1/4 inch on both sides of the line and then cut on the diagonal line. Square each of the resulting 1/2 square triangles to 3 1/2 inches. Press toward the darker fabric. Arrange as in the photo at the top of the tutorial and sew the squares together to create the block.