You will need:
Diana F+ camera
20mm Fisheye lens
20mm Fisheye viewfinder
Remove the regular Diana F+ lens by aligning the dots on the camera and removing the lens.
Attach the 20mm Fisheye lens to the Diana F+.
Make sure that the two dots are aligned before you twist the lens.
Attach the 20mm Fisheye viewfinder.
Make sure you twist the wheel to lock the viewfinder in place.
You are now all set to take Fisheye shots with your Diana F+