By default, headers & footers are turned on in Pages' word processing documents. They are not on by default in page layout documents. In either kind of document, I prefer to show the layout so I can see my document margins & the headers & footers. You can adjust the settings in the document inspector.
To put the page number on the right side of the header, use right-justified or a right-aligned tab & then insert the page number from the Insert menu.