Every site header shows a search form that lets you find pages in that site. In the search form, type the words you want to search for and press Enter.
You can search all of Wikidot, including private sites that you are allowed to read, at http://www.wikidot.com/search:all. Global search works like basic searching, with these additional options:
Note: searching on tags is currently not enabled for performance reasons. When we've solved those, we'll enable tag searching.
In basic and global searches you can additionally search for pages that have specific tags: