It's easy - just select the desired access level, copy this link and send it via email, instant message, etc.Link: Just a link to your wiki. Post this anywhere and people can ask you for the invite key.
"A wiki is a type of website that allows users to easily add, remove, or otherwise edit and change some available content, sometimes without the need for registration," according to Wikipedia -- itself probably the most well-known example of a wiki. Wikis are public (or semi-public) collaboration spaces, and as such are well-suited to group work.
For this class, you'll use the wiki mainly as a tool for group collaboration, although we will use it for some classwide activities as well.