Good evening all!
I like jME!
Secondly I would like to join a project.
To create his own project sounds cool, but alone you are…alone. 
I would say, I 'm at the medium level of java.
In jME I'm a beginner.
To learn and know more of jME I would like join a project, maybe MonkeyWorld3D.
Any suggestion
I suggest going through the flag rush tutorials. Its the best way to get started.
There are a number of projects announced in the forum that are requesting programmers, try searching the forums for something like help requested…
Welcome to the community.