Step 1: Materials
Glass jar with lid or cork
Pebbles or gravel
Spoon or funnel
Water spritzer bottle
Some notes on finding supplies
Activated Charcoal: Your best bet for finding activated charcoal is an aquarium or pet supply store. They sell this charcoal in bulk packages. This is the type of charcoal used in Brita filters and air filter masks as well. You only need a few tablespoons of the stuff for one moss garden.
Peat Moss and Potting Soil: These are common and can be found in at most garden centres.
Pebbles: You can find pebbles on the ground, or you can buy them in a store. Aquarium stores sell pea gravel that is the perfect size. The stones should be quite small, about the size of lentils or raisins. You need enough pebbles to create a solid layer in the bottom of your container. Wash your pebbles well before using them.
Step 2: Find a bottle
Once you start looking, you will see bottles everywhere. You can recycle old jars or bottles from your house - salt shakers or clear glass spice jars work well. I like to find bottles in thrift stores or garage sales, or rescue them from the garbage.
I recommend a wide-mouthed container (such as a canning jar or spice jar) to start with - it's a lot easier than one with a narrow neck.
The bottles that work best are ones that have a tight fitting lid. This helps to keep moisture inside the container.