Make sure you add your server credentials to your API calls, otherwise you'll be getting 401: Unauthorized responses from your server.
Before you can manage your game server, register it by POSTing to the /dedi/register endpoint with a secret.
Create a game session by POSTing a settings object to /dedi/. This returns an object containing your game's ProcessId. Use that ProcessId to get updated information about the session (such as time left, number of players, ...).
It is recommended to have a maximum of 5 sessions per machine.