4. Protect pages
Single pages can be protected by administrators from unwanted changes, e.g. if pages contain especially important information, or changes could lead to severe damage to the wiki. It is e.g. very common to protect the main page.
You can find the function Protect in the right navigation bar in the tab Tools.
By the way: users tend to protect pages from other users. The problem is: every wiki lives of publicity and the attraction of this publicity. So a wiki with many protected pages is not a wiki anymore. So make sure that you don't protect too many pages!