What's the difference between a Master Page and a page?
What's the difference between a Master Page created in Master and a page created within Stage?
A Master 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 Stage would have different sections that a user could navigate to and include links to your Master Pages. Please note, that this linking needs to be done in the Catwalk of your project and can't be done through the page editor.
For example, you have a page called Women that has all the products targeted at women and users have the ability to add those products to a Cart which they can see a link to on this Page. If the user wants to open the Cart, they can click on the icon and they would be taken to the cart Page which would have been created within the Master App.