Try this link: InDesign Help | Add basic page numbering
Also, you must have the master page applied to the document pages. You can tell which master page is applied to which document pages by looking at the pages pallet. As you can see in this screenshot, I have made two master pages (A and B). Master-A is applied to pages 1-3 and 7-8. Master-B is applied to pages 4-5. The master page called None is applied to page 6. None is the master you would use if you didn't want anything from the master pages on your document pages. To apply a master page to a document page, either drag the master-page icon onto the document-page icon in the pallet, or make a selection of document page(s) in the pallet (click to select a page, shift-click to include more pages into the selection and Command-click to deselect pages from the selection) and go to the fly-out triangle and select Apply Master to Pages (or just Option-click on the master icon of your choice).
