Every pilot, at some time or another is a "virgin" on a particular aircraft or at a particular airport. The only way to get experience is by doing it. And the only way to do that is by flying as a trainee on many flights. I'm not certain what the requirements are to be "rated" on a 777, but I am certain that a lot of "trainee" hours of flying it are required, in addition to lots of hours on a simulator.
My post on another thread.