Yes it's all done simultaneously, you don't have time to wait for the other guy to do his scan before starting yours. Come together for the briefing and any problem solving or things that need discussing.
But I wouldn't start worrying about that yet, just learn the scans and memory items and try to get a general overview of where the switches are and the approach profiles for different scenarios. That'll help you greatly. How to put all the flows and scans together will be taught to you.
Also look at smartcockpit.com