I think you might get a more "concrete" idea of how to do this by looking at what others have done and documented, i.e. research. The most widely cited model for collaborative online learning is the Community of Inquiry: https://coi.athabascau.ca/coi-model/
There are 3 Open Access research databases for online collaborative learning and teaching projects that I know of (there may be more):
Moodle's own: http://research.moodle.net/mod/data/view.php?id=1
Athabasca University: http://www.irrodl.org/index.php/irrodl/index (I'm a grad student there)
The European Union: http://www.eurodl.org/
A broader search of the web (add filetype:pdf to search queries to get more results as research papers) can return some interesting results too.
On using Moodle per se, there are some great "How to" style books available to get you started. Check with your favourite book vendors. That's about as good advice as I can give with the information you've given.
I hope it helps!