A high-level tour of the WikiVerse
Completion requirements
4. Anatomy of Wikipedia's main page
4.3. The lower menus
Other areas: The Community portal lists opportunities for interaction. If you want to help & don't know where to start, scroll down to the Help out section.
Sister projects: we'll be talking more about these.
Licence: usually CC-BY-SA but some items (images especially) may have additional restrictions.