As you can see you can give the application that is accessing you different keys than the ones you use to access your target CiviCRM.
So in this example I will explain to the party wanting to access my CiviProxy that they have to use the key 1234#tsT#eR1k and the api key eR1k!tSt4321. My target CiviCRM will expect site key p1P0!tEst1Ng5678 and the api key cal1Mer0#tST.
As of now, the documentation at https://docs.civicrm.org/civiproxy/en/latest/configuration/ is not clear.
It is not explained where API-key and site keys are obtained from the CiviCRM-installation in this para: