Measure the size of your windows. Purchase fabric (thick) and blackout material. Include a few extra inches for the blackout material, and at least a foot for the fabric. Measure out and cut both the fabric and blackout material for each side of the window (half of what you measured, length wise).
Place the blackout material over the fabric (have the side of the fabric that you want visible facing out). Fold the edges over and pin them. Then, sew them in place. Be careful, as the piece is usually quite large, and can tend to stretch.
Cut out two pieces of strong wood in 6x6 inch blocks. Drill a hole in the center, the width of the wooden rod.
At the top of your curtains, use the puncher to put in the grommets. The length between the grommets depends on the width of the window, how many curtain hooks you have, and how heavy the curtain is. I did seven inches in between, which proved to work. Make sure that the nice side of the grommet is on the fabric side of the curtain.
Hook the shower curtain hooks through the grommet holes. VERY IMPORTANT - make sure that the shower curtain hooks are wide enough to comfortably fit around the wooden rod.