-glass container w/lid
I found all of my items at a craft store and found the moss while on a walk in the woods.
1) Take yourself on a nice long walk and bring a container and something to dig the moss up with. I used a regular spoon.
2) Wash your glass container with warm water and soap. Dry the container and make sure it's free of all soap.
3) Fill the bottom of your container with a layer of rocks about an inch thick. The rocks will help with drainage and water management. (I read a few places that suggested placing a thin layer of activated charcoal over the rocks to help deter the growth of bacteria which can be important to keep closed terrariums from smelling. I decided to forgo this step.)
4) Cover the rocks with a layer of spanish moss. The spanish moss acts as bedding material and keeps the soil separate from the rocks.
5) Place a thick layer of potting soil over the spanish moss. Do not use fertilized potting soil. Fill the jar to about 1/4 - 1/2 of the way full.
6) Arrange your moss. For bigger containers you can also plant ferns and small plants along with your moss.
7) Decorate your terrarium. I found a cute little corgi figurine for my big terrarium. The small terrarium has a rock in it that the moss was actually growing around outside. Etsy.com has some great ceramic houses, figurines, gnomes, etc. I'm going to make a few more terrariums for friends and family and might buy some items from etsy to make them super cute.
8) Long term care is very easy with closed containers. Do not place in direct sunlight. You only have to water it every 2 - 3 weeks. As long as the terrarium is moist it will continue to self water (the water will pull up from the rocks and form a mist that will then drip down). Water when you notice the soil is drying up.