There is not so much to say. If you know the FLOSS community and the common development method, you are ready to the Noosfero development. The Noosfero born in 2007, by the Colivre (a Free Technologies Cooperative)'s team, and that was created to be free (as in freedom) software from the beginning. That is written in Ruby, using the framework Ruby on Rails.
If you want to collaborate with the development, clone it's Git repository, write in the coding conventions, and send your patches!
Don't know where to start? May you want to see a list of items (bugs or features) that are easy to solve.
Have any Questions? Ask to the development mailing list. That is really important to be on this mailing list.
You may also want to read more about the Noosfero development.