For free school sites you can only have five buttons that link to custom pages. Any additional buttons that you add can only link to modules such as the guestbook, calendar or enquiry page for example.
However this does not have to restrict you to only having a few pages. Don't forget you can create links to other pages within the content of the page itself, or create index pages that link to lots of other pages. There are lots of ways to interlink your pages, so don't feel you are restricted just to the pages that link from the navigation button.
Community Kit websites and Premium School websites can have up to 13 buttons, and these can link to any number of custom or module pages.