A wiki is a free anybody-can-edit web site. Anybody, even you (yes, you) can add text to pages, edit pages, even create new pages. Pick a topic (or invent one), go to the topic page, click on the edit link [Edit text of this page] at the bottom of the page, and you are an instant Web author. Click on RecentChanges to see the latest entries.
This wiki (there are many others) is about getting answers to questions someone else may already have asked. It's a FAQ sheet, a list of Frequently Asked Questions, quite often matched by useful answers. The Table of Contents, or List of Topics, is on the HomePage.
How can a wiki work at all? Here are some thoughts, from well-established wikis --