Environment variables allow you to provide values to your application. These values can vary from environment to environment. In addition to the ones automatically injected, you can also define your own environment variables.
Add and Update
Configuration tab, you can see all the environment variables that are available to your application. This is a very useful resource when developing your application to ensure you are referencing the correct names.
Update Configuration in order to add or update your own. Make sure to mark sensitive values so that users without proper access can't see the values.