I have no Link for the pincushion and so I will show how to do this. (I learned it in my patchworkclub)

1. This is the finished pincushion.
2. You need a white and a second square. In the second square must be an opening.
3. Sew both (right sides together) and turn through the opening, then sew along the black line (this line shows also, how big the pincushen will be)
4. Iron it as shown and stich the white parts down (this is a bit tricky)
Stich the corners together and fill through the opening, close the opening and add a button.

For cfidl: If you want to make a pillowcase from the squares you must at first instead of the opening add a zipper along the dark blue squares.