A dynamic page is a type of page that can be linked to from any page and creates the basic layout of that page. It also creates the default layout of pages that could use the same structure but with different data, for example, a product details page.
Whereas a page created in the site builder would have different sections that a user could navigate to and include links to your dynamic pages.
This linking needs to be done in your project's repository and can't be done through the studio.
Example use case of dynamic pages
For example, you have a page called Women that has all the products targeted at women, and users can add those products to a cart to which they can see a link on this page. If a customer wants to open the cart, they can click on the cart icon, and they would be taken to the cart page, which would've been created within dynamic pages.
You can also set up dynamic pages for different rules. For example, you can set up a default dynamic page for the product details page, but you can create a dynamic page rule that will show another page for any products over $500. So you can tailor dynamic pages for particular circumstances.
When you first open Dynamic pages in the studio, it could be empty. This is because a schema needs to be created by a developer first. See the developing a dynamic page extension article for more information.