If you need to add page numbers to a long document, you don't want to have to do it manually. Inserting them individually on every page would be an awful way to spend your day. Instead, you can put a special icon on the master page which then appears as a number on every page it's applied to. You can add numbering icons to any master page you want, and you can format them with paragraph styles or the control bar. This will save you doing a huge amount of unnecessary work.