Step 1: Materials
Step 2: Cutting
Step 3: Put it together
Put the third cup on top of these two so that they face 'mouth to mouth'. (see images)
Step 4: Place on the camera
Step 5: Taking photos
Exposure can be done using levels according to this other instructable.
Here are some sample photos, as you can see this lens gives a unique experimental look as the images are taken using a magnifying glass which is not intended for photography.