How to play or create coop missions?

[Kord]

I second the question. How come it is not possible to launch any multi mission, like the stuka assault on ships, and just join in 2 of the planes with a friend?

Or is there an easy switch on the mission editor to enable this on any mission?

Or perhaps we do something wrong? Realism stuff is set right, server connexion is ok for both guys, still no way to share a Lan flight. The second player sets the right army but cannot jump in any plane...

Thanks for the help.