The Data Library in Bravo is where you set up the API requests.
For example: If you want to display a list of items from your Google Sheets in your app, you first have to retrieve the data by setting up a request. Then, Bravo receives the data from the request and it's ready to be connected to an app.
Data Binding is where you connect the requests to your app UI. To enter Data Binding mode: open an app project, click on an app screen, then you can start binding.
For ex: Once you retrieved the list of menu items from Google Sheets, you would click on the app screen with the menu design and bind the data to the respective UI element (i.e. bind the menu item name to the text box in your design).