When it comes to terrariums, you have a few types of plants to consider, but two dominate the houseplant market - air plants and succulents. However, if you aren't a plant nerd, it isn't obvious ...

Bury your plant into the soil you've added to the terrarium. (You may need to use some long tweezers to do this). Finally, add some water to it to keep the soil moist then seal the jar.