Two pages getting 'locked or linked' together, why?

The page layout mode automatically creates a separate section for each page, word processing does not.

This is a very common question. Pages doesn't "see" a page as you & I do. Pages sees logical pages, separated by section breaks, rather than physical pages. You can see this by showing thumbnails, View > Show Page Thumbnails, & then clicking on a page thumbnail. The yellow border around groups of pages shows the logical page. You need to insert section breaks before & after the physical pages to separate them.

It probably means you're using a word processing document, not a page layout document. What does the title bar of your document say next to the name of the document? Here's a screenshot of the title bar of a Pages word processing document.

You can't change a Pages document from word processing to page layout or vice versa. You can, though, copy & paste everything into a new page layout document. But I don't see any reason to go through all of that. You can do all of the things in word processing that you can in page layout. The only difference is the underlying text layer in word processing. Until Pages 3 there only was a word processing mode with the default text layer. A lot of users here had problems ignoring that text layer when they were doing object-oriented projects. I believe that is the main reason the separate mode was introduced.