To add content to your marketplace, you can create and edit new static pages (learn more about Pages and learn how to edit them). If the new page you want to create shares a lot of similarities with an existing one, it can be faster to copy it.
To duplicate an existing page:
Find the page you want to duplicate
Click on the context menu ("...") for that page, and click on "Duplicate page..."
Give your new page a unique identifier
Click "Duplicate page"
And voilà! Instead of starting from a blank slate, you can instead edit the content that was on the page you've used as a source.