The first section in the application builder is called the "Application Map". This is where you will define the core structure of your application: the different pages of your application (e.g. Home Page, Profile Page, Login Page...).
For each page you will be able to configure the main settings (page name, url...) and SEO settings (Search Engine Optimization) by specifying which title and description should appear in the search results (in Google for example) for the page. There can only be a single root page (the page the user will reach first when he connects to your app).
By default, when you create an application, a Home Page is created with the root status. You can later remove this page or change the root status.