I commute so use staff travel in T5 all the time, its very easy to do!
Check in for your YVR at any self service kiosk, if you dont get a seat (usually the case) head up towards the north end of T5 (Zone A) where you will see a door located adjacent to Cafe Nero, go through the door and follow signs to staff travel, you will see a waiting room with on the left with loads of info screens, just wait in their till you see your booking reference on the screen and it says something along the lines of "accepted" beside it then proceed to the room oposite where you can get ya boarding card and check your bags in.
if your travelling on paper tickets (not sure we still do them for BA staff travel) then you'd prob have to check in with check in assistance or at a self service bag drop