You probably have a E(electronic)-ticket. You can NOT go directly to the gate, you need to obtain your boarding pass first!!!!!!!!!!!!!!!!!!!!
Check in curbside (may be a charge for this, plus tip, depending on the airline and/or airport) or at the counter inside the terminal. This is where you check your luggage, too. You need to show a government-issued ID, no matter how you check in.
Proceed with your boarding pass and your ID to/through security. You will not be permitted beyond that point with just a voucher, even if you had one. You gotta have the boarding pass.
ETA: I went back and forth on whether to post the following and finally decided I should... Please consider using a different Travel Agent in the future. I'm EXTREMELY uncomfortable hearing that a supposed travel professional would tell you you can go directly to the gate using a voucher. In fact, I'm so uncomfortable with the response you got that I'd suggest calling US Airways now to make sure you HAVE a reservation, and that it's the itinerary you thought.