You will need:
from color A(pink): cut two 4 7/8" squares and one 4 1/2" square
from color B(black): cut two 4 7/8" squares
from background (white): cut four 4 7/8" squares
Draw a line with a pencil down the center diagonally on the wrong side of each background square.
Place a 4 7/8" block from color A, RST (right sides together) with a background square, then stitch 1/4" from the pencil marking on both sides. see photo below. If you don't have a quilting foot, I highly suggest getting one, because the foot is a perfect quarter inch for all your quilting needs.
Repeat with the other 4 7/8" square from color A and also both squares from color B.
Cut down the pencil line with a rotary cutter and you've got 2 half square triangles.
Half square triangles are used all the time in quilting, and now you know how to make them. :)
repeat with other 3 squares, then press the seam towards the colored triangle on each square.
set our your squares like this, so you can see what you're block will look like:
Sew them in rows
Press the seams on each row in opposite direction as the next. This will allow your seams to lay flat when you sew your rows together.
Sew the rows together matching the seams, and trim your block down to a
12 1/2" square if you need to.
Now, go hide it somewhere safe, so it doesn't get used as a dolly blanket and end up with chocolate stains on it... what? that's never happened to you? ;)