To make a terrarium, you need a fairly large jar or glass container with a lid. You put in a layer of large rocks at the bottom and then cover with charcoal. Then add some soil on top. Put in your plants (succulents or ferns) and then add some moss and rocks and maybe a little fairy. Give it a spritz of water and close it up.
The terrarium will recycle the water to keep the plants hydrated. And we learned that while plants take in carbon dioxide and expel oxygen during the day, they reverse at night so they will always be able to breath. And as for food? as plant material breaks down there will be plenty of nutrients!