A home-crafted terrarium is the best option for growing moss indoors; moss, a woodland plant, needs a humid, moist and partially shaded environment. Almost any glass container can serve as a terrarium as long as you can fashion a sufficient cover for it to keep the water contained.
Create a terrarium. An empty fish tank works well, however small; even round goldfish bowls can function as simple terrariums. Or, you can make a striking terrarium by using a clear-glass cake stand and cover.
Use small foil baking pans to hold the soil in your terrarium. You can find these in various sizes and shapes, and they will help your terrarium to be mess-free and leak-free. Purchase the size and shape that best fits your terrarium container.
Gather woodland moss. If you have a wooded area nearby, take a walk with a tray filled with damp paper towels. Use your fingers to loosen patches of moss around the edges, then lift and loosen with your fingers until the moss comes away from the soil. Be sure you have a good amount of roots hanging down from the moss; they'll probably be thin and not very long.
Fill the tray(s) with a good soil mix, water thoroughly, and gently place your moss patches over the wet soil.
Cover the terrarium base with the cover. If you're using an old aquarium, use a piece of glass to cover the top. You can also use clear plastic, but glass is more attractive. You can have glass pieces cut to size at a local framing or glass shop for a very low cost.
Set the terrarium where it can receive some light but not full or direct sunlight.
Watch for growth and health. A well-designed terrarium won't need additional water, as the water droplets are contained and will simply run back down the sides of the terrarium. Keep an eye on things the first few weeks, and if the soil gets dry, add more as the tiny ecosystem adjusts itself.