Always remember the day you really started to learn to drive was the day you passed your test and started to take full responsibility for your position. The same works in flying.
Alot, and I mean alot, of the Co-Pilots I fly with know alot more about the systems and the technical side of the aircraft than me but, to be honest, they don't know how it flies like most of us crusty buggers do and it takes a while to learn.
Most important though, never be afraid to raise a question, concern or objection. If the other pilot has a reason then you'll get it, if they don't you may just prevent them from making a pigs ear of it.
Good luck.