After you have registered in your account, you can proceed to setting up the application.
1. Install the Outline application through the App Store:

2. Configure the application.
We go in your personal account.
In the Account tab, select the server and click "Copy key":
and add the configuration to the application by clicking "Add server".

I advise you to select each server and add it to the application in the same way.
3. Run the application
Select the server and start by clicking on the "Connect" button:

Done.