Any clear glass container (plastic can also be used) with or without a lid can house a terrarium (it all depends on the plants you are using - ie: succulents cannot be grown in a closed environment) Bright light is best - but never direct sunlight!
The first few terrariums I built had to be taken apart and redone with all new materials (save the decorative elements, which I scrubbed off with soap and water) because I introduced too much moisture into them right from the onset and they were quickly overrun by mold - the terrarium's mortal enemy.
After further research, I rebuilt from the base upwards using:
1. a layer of rocks for drainage, (the dollar store)
2. one inch of activated carbon (you'll find this where they sell fish & aquariums) - this helps filter decaying plant matter,
3. layer of dry sphagnum moss (stops soil from falling through to the rocks below and allows you to 'sculpt' your terrain)
4. approximately two inches of prepared all-purpose potting soil (don't use dirt from outside!)
5. plants which I'd trimmed right down, removing most of the roots and dirt surrounding them,
6. decorative elements,
7. a few ounces of water (preferably not tap water) sparingly applied and a few good mists of water.
Many of the rocks I used were collected by my children more than fifteen years ago, when we lived in Peace River. As well, the merino glass piece behind the couple on the bench was a pendant that fell (& chipped) a few years ago. Terrariums provide the perfect opportunity to dust off and display those cherished items that have been languishing in a cupboard or drawer in your home.
The little people were purchased at a hobby store which caters to miniature railroad enthusiasts. Everywhere I go now, I find myself keeping an eye out for interesting objects that could possibly be used in my next terrarium.