First step: Find a container. You need something that is watertight. It has to hold small granules of sand and water. I looked all around and eventually found this square tin container at Canadian Tire. It has little handles and was just big enough to sit in the middle of my kitchen table.
Second step: Find the sand. This was harder than I expected. After trying both gardening shops and hobby shops I finally found some in the pet store in the aquarium section. They had different sized granules but I wanted it to be pretty fine so that the rake would work well.
Third Step: Find the rocks. I was originally just going to go outside and see what I could find, but while at the pet store they were selling the kind I had envisioned in my head- perfectly round ones. So I picked up a couple there, and felt a little silly paying for rocks.
Four step: Find moss and tools. Moss is actually not easy to find. After multiple attempts and debating whether to get artificial moss or not I ended up getting the real stuff at a Country Blooms Nursery. There are, in fact, 22,000 kinds of moss worldwide. I ended up getting Scotch Moss and I love the look of it. My small garden tools I found at Peavy Mart. I saw them when I was buying terrarium items and had them in the back of my head for a Zen Garden. They are the perfect size and all of my kids were very excited seeing them.
Fifth Step: Put it all together. I put a layer of sand to cover the bottom of the container. Then added in my rocks and twisted them ever so slightly to help them sink into the sand.