How to start?

Hello!
This huge (5 Liter) lab-bottle is in my room since serveral years. In the past it was used to collect coins but as i took them to the bank some days ago it is now empty – and because i like moss i started about thinking to convert it to a mossarium.
The problem: i have absolutely no clue in how to start. Which materials i may put in, which local (Germany) moss and perhaps other plants (fern? flowers?) could be used.
Therefore i appreciate any input.