Hi Paul,
Pages produces two types of document: word processing document, and page layout documents. A quick way to determine which type of document you have open is to look at the Insert menu.
If the first item in the Insert menu when your problem document is open is "Section," your open document is a Word Processing document, and if the insertion point is in the text of the document, the page break and section break items should be 'black'.
If the first item in that menu is "Page", your open document is a page Layout document, the Page bd the Section break item will not appear on that menu.
From your description, and from your statement that you "insert a text box where I type the content" I would say you are working in a page layout document.
In a page layout document, every page is also a section.
Page layout documents have no Document Body, which in a word processing document, carries the main stream of text running through the document.Without a Document Body, there is no place to put a page break. And with every page also a Section, there's no need for Section breaks either.
If you want to insert a new Page (and a new one page section), open the Insert menu and chose "Page" You will add a text box (or other container, such as a shape) to the page if it is to have any text on it.
Form longer documents where text will run from one page to the next, a better choice is often a word processing document, where you do not have to manually add pages. WP documents automatically ann a new page as the ne you are working on becomes full.
Regards,
Barry