Its basically whatever you want it to be. If you want to take towns and bases then by all means give it a shot. If you want to fly historical type missions with a set objective of fighter sweeps, interception, bombing missions, CAS for a GV squad then go for it. Try to find something that you can immerse yourself with in a role that you like. Try hooking up with a squadron and working with them either for or against a staged mission.
Sometimes you will see threads here for the Allies or Axis stating that they are going to run a mission on a specific night. Try to get some basic ideas of their intended target. Most CO's will give you the target of a bombing raid, but its up to you to stop the raid and many guys in here can plan some doozy raids for you to try and stop.