Hi,
For Login, transaction key and return url setup, find the below screenshots.
Return url format: http://yoursiteurl/?q=cart/egrfirstdatae4h/complete
Transaction type: if you select sales it will capture the payment instantly from customer account or for select authorization it will authorize the order and you can capture the payment later from your Firstdata account.
Transaction mode: If you live Firstdata account you need to select live mode or choose test mode.
Thanks,