Apologies if this is obvious, but I'm new here. I see the term "community wiki" bouncing around a lot and have no idea what it means. Maybe my reputation is not high enough to have access to community-wiki features?
Community wiki is just a way to let (almost) everyone edit questions and answers. There's a check box at the bottom of the question and answer input box to select community wiki. Currently, you don't have enough rep to edit community wiki posts, but that will change very soon. See the faq.
One other feature of community wiki is that no one gains reputation for questions or answers marked community wiki (which makes sense since multiple people can edit it).
Community wiki is especially useful when a question has no real right answers. For example, this question is community wiki.