It’s easy to make your own decoupage glue. It’s also a lot cheaper than buying it already made. For basic decoupage projects you can mix 3 parts white “school glue” with 1 part water. This gives a finish similar to what you get with basic Mod Podge.
Use several coats of the mixture being sure to let each coat dry thoroughly before applying the next. Several layers of decoupage glue will make it more durable. When finished with the coats, seal with an acrylic spray. Choose the type of acrylic spray for the type of finish you want–matte or glossy.
You can use one part glue to one part water for gluing paper items onto something & then seal it with the 3-to-1 mixture if you like.
Try these out on some practice papers first to see if you like the effect. You can adjust the proportion of water to school glue if you like for you project’s needs. The original recipe makes a decoupage glue the consistency of pancake syrup. It seems a bit thin, but it dries to a hard surface.
An easy project is taking plastic eggs and covering them with papers. You can make pretty eggs as shown here or make anything you like. Another easy project is to decoupage a picture frame. Small table tops are other good projects.