Basically a garden in a jar.
Here's what you'll need.
Good potting soil
Rocks for the bottom to help with water drainage
Plants that require low light and little water
and if you want to add figurines to make it a little more interesting.
Start by adding a 1" layer of pebbles to the bottom of the jar followed by a 3"-4" layer of potting soil. Now you'll start adding in the greenery. If the plants are too large for the jar you have chosen, simply split them just as you would if you were splitting plants in an outdoor garden. If the lid to your jar is narrow and difficult to fit your hand into, use chopsticks or a bamboo skewer to move the plants around.
The above terrarium I made is just simple, with one plant in there.
This one, I wanted to add a figurine to just to give it a bit of distinction. I took a man from my kids farm toy and added it as if he is working among the "trees."
Now water your terrarium lightly (until you can see some moisture down in the pebble layer), and put on the lid if you are using a jar that has one. You will need to water your terrarium every few weeks. Droplets of moisture are fine — you want to see these — but if it starts looking especially foggy in there, take the lid off for a few hours to let moisture escape. Otherwise, an occasional water and/or spritz with a spray bottle should be fine.
And there you have it. An inside garden to brighten your spirits in this otherwise bleak season.