I keep seeing these posts everywhere on how to do these little terrariums and I saw the idea 2 years ago at a craft sale and just took my time getting around to doing it. So here's my version, always simple!
Find the plants you want to use: I had a spider plant from my mom and I had some moss outside (you need to make sure you pick plants that can handle these conditions of course)
Put a little soil in the bottle, and then some rocks, then your moss, and put your spider plant (or whatever other plant you pick) off to a side, a little bit on it's own, making sure the roots are in the soil.
Put a little bit of water in and there you go! Pretty easy right?
The this one (above) is still waiting on it's spider plant but I needed it to grow roots first (below) so when that's ready it will go in there too.