I thought I was the dumd.! But at least you kept trying I gave up!I would love to have one just can't think anymore.
After the zip is stitched to the stabiliser, the next colour stitches the fabric to one side of the zip. When you flip that over, the outline on that side of the zip will be covered with a double layer of fabric. Repeat with the next colour for the other side.
Good luck.
You're not 'dumber than dirt', just lack experience in this particular project. You'll be an egg-spurt soon!
After the zipper is stitched to the stabilizer, lay one piece of fabric face down with the middle of the fabric along the zipper. The next color stitches the fabric to the zipper. Then fold the fabric up out the way and do the same with the next fabric piece, but after stitching, fold the fabric down. Hope this helps.