Getawaytoday does not send you anything for your ticket into DLR. (except maybe an email confirmation/receipt) It is an E-ticket, like for the airlines. You go to the ticket booth with your ID (make sure it matches the name on the ressie) and get your tickets there. You then take your tickets to the turnstyles and enter DLR! You can also pick up your tickets before you actually want to go into the park - like if you get there the night before and want to have your tickets for the next day - they aren't activated until you go through the turnstyles.
HTH