About page templates
App Builder page templates are predefined layouts that can provide a basic start in
creating a project.
When you first start to create an App Builder project, Page Templates is one of the options provided on the New Project page of the Designer. These templates are designed to provide a good variety of basic layouts for you to use in creating your app.
Each page template consists of a number of Flexbox components arranged in common layout patterns. Pick the patterns that most closely matches the basic layout you want to use for your app. You can later rearrange to the basic layout, add or remove Flexboxes, and change the dimensions of the Flexboxes according to your app's needs.