You can use the Connect call to start the authorization process. If authorization is successful the OnConnected event gets triggered and you can start calls to access the service API.
TMSFNCCloudGoogleGmail1.Authentication.Key := 'abc';
TMSFNCCloudGoogleGmail1.Authentication.Secret := 'xyz';
TMSFNCCloudGoogleGmail1.Authentication.CallBackURL := 'http://localhost:8000';
Please have a look at the CloudStorageServiceDemo for a full working example.
Other components in the TMS FNC Cloud Pack work in the same way.