Here is a tour of the most important help pages:
HelpForBeginners - if you are new to wikis
HelpOnNavigation - explains the navigational elements on a page
HelpOnSearching - explains the search functions
HelpOnPageCreation - how to create a new page
HelpOnTemplates - how to use page templates
HelpOnUserPreferences - how to make yourself known to the wiki, and adapt default behaviour to your taste
HelpOnEditing - how to edit a page
HelpOnActions - tools that work on pages or the whole site
HelpMiscellaneous - more details, and a FAQ section
These pages contain information only important to wiki administrators and developers:
If you don't find what you're looking for in the above, try these:
HelpIndex - An automatically generated index of all help pages as a flat list.
HelpMiscellaneous/FrequentlyAskedQuestions - answers to frequently asked questions.
If you find any errors on the help pages, describe them on HelpErrata.