Install
1. Set up a Drupal 8 Website
2. Enable the DrupalGap 8 Module
3. Install the DrupalGap SDK
Go to your Drupal root folder and run the DrupalGap install script, or you can manually install the SDK.
cd drupal
./modules/contrib/drupalgap/scripts/install app https://www.example.com
This will create a folder called app, place the DrupalGap SDK inside of it, create a settings.js file for the app and then set the sitePath variable to https://www.example.com.
Done
This sets up an empty web app. You can easily add other types of apps later, all with only one set of code.
Demo it in a browser by visiting:
https://www.example.com/app