If you're using the "Deluxe" version of Website Maker by any chance, you would just introduce another navigation system into one of your pages and have to actual levels of navigation - a higher one to navigate around your general site and one navigation below that to navigate around the sub pages under one of your pages. That would probably the most elegant solution to the problem.

However, if you're not using the "Deluxe" rate, there's still a pretty good way to go about this. Just add more pages to your project using the "New page" function in the "Pages" panel. Fill the pages with content. Highlight the navigation and go to the "Properties" panel. Under the "Navigation" section you can set the new pages to invisible if you don't want them to show up in your website's main navigation. If they're not part of the main navigation, there will obviously have to be some way to get to those pages. So, what you can do is placing internal links from your initial page to the following ones. Just put in a text or graphic link that e.g. says "Next", select the element, go to the "Properties" panel and set up the internal link under the "Linking" section, with the link pointing to the invisible page.

I hope this helps.