Every wiki starts with a Home page. Usually this would look like a quick intro or a set of links to the other important pages, but the format is freeform. Traditionally, wikis are made so that every page is reachable from the Home page, but that isn't a hard requirement.
Pages can be grouped into folders by adding the folder name as part of the title. For instance, creating this page looks like
which creates a page named "Wikis" in a folder named "Features"