A Wardian case is the predecessor of the modern terrarium. A terrarium is an enclosed ecosystem of plant life, normally made from glass or plastic to let light in. Terrariums aren't limited to plants, some even house small reptiles!
Wardian terrariums have an interesting history dating back to 1829, when Dr. Nathaniel Bagshaw Ward made use of an enclosed glass case to grow his ferns. He did this because they were being poisoned by the air pollution in London. He later used the same type of "Wardian case" to ship plants to and from Australia.
They come in all shapes and sizes. The old-style Victorian cases are lovely unique pieces of furniture that let you bring some wildness into your home. It's another take on indoor gardening that adds a whole other dimension and boundless opportunities to experiment.
There are a number of new models that are retro-styled to look like the old ones. These you can buy online and get them delivered.
There are no hard and fast rules of what you can plant in a terrarium. The size of the case will restrict what you can grow in your terrarium, but apart from that your choice is restricted only by your creativity! Terrarium gardeners often add some decor to their terrariums -- possible small figures, stones, tree trunks or aquarium decorations.
Terrariums are easy to look after. In fact, they are known for thriving on neglect and can go for long period with no care at all. I'd suggest reading up about any special requirements of the plants you intend using in yours.
Keep it out of direct sunlight to prevent the plant from burning. Because they're enclosed in glass, the heat doesn't escape easily and can get too much for your plants.