Mercantile theme is based on Child/Parent Page Concept. Parent page will be the selector and its child page will appear on the front end. For example, if you want to make the Team Page, Give the name of the parent page(Example: Our Team) and other team members information are as child page. And if you select that Team Page on the widget, its child page will appear on the front page. Please have a look how it works from the demos.
Hope you understand what we mean. Let us know in case of confusion.