What sort of missions would there be for someone like me who has 4-5 freinds playing multiplayer, and what actually happends when you get shot?
Mission vary from coop to pvp and scenarios are really diverse though the most popular (unfortunately) is domination type games.
Domination is basically your team against the AI on a whole map with random missions, it's not really that interesting.
I personally play ARMA 2 with a french team and we do mostly coops missions.
When you get shot it depends on how the mission was made. Sometimes you can be revived (with a limit to the numbers of time you can be revived) and sometimes it's permanent death. It can also be a mix of both: if you aren't treated in a limited time you die.