An eyepiece is not necessary to see objects, but it helps to keep your eye off of the viewing lens. It can also make viewing more comfortable. Use a drill or sharp object (e.g. scissors) to make a hole in the bottom of a film canister. The hole should be in the center of the canister and large enough to slide the smallest tube through. Line the smallest tube up with the hole in the canister. Push the tube so that the top (side with the lens) inch is inside the film canister. If the tube will not fit, make the hole larger until it does. Use glue or liquid cement to keep the eyepiece in place. This will allow you to look through the eyepiece without it moving. Give the glue time to dry.

Summary:
Make a hole in a film canister. Push the lens tube through the hole. Secure the eyepiece.