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
HelpOnEditing - how to edit a page
HelpOnActions - tools that work on pages or the whole site
If you like something for a presentation, look at WikiCourse.
These pages contain information only important to wiki administrators:
HelpOnAdministration - how to maintain a MoinMoin wiki
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.
FrequentlyAskedQuestions - answers to frequently asked questions.