Looking to play with friend against NPC/AIs (ie: PvE)

[Woke Up Dead]

Good advice here, but since you appear to be new to IL2 I'd go with Marabekm's suggestion as it's the simplest one:
* Make sure you all have the same game version (4.13 is probably best and has most planes)
* Practice with your friend in a dogfight mission against AI so you can get the hang of flying together and communicating
* Try a "real" mission in co-op where you only get one life each

Maybe someone could suggest some good beginner dogfight and co-op missions on Mission4Today.

[Marabekm]

Well for the beginner coop mission, I would just go with one of the stock ones that everyone already has. The IL-2 attack on ships in the gulf of Finland is good.
It has both sides available, so just make sure everyone knows to go the same side, and then you could play it again and everyone goes other side.

(Stay away from the TB3 night/dawn bombing mission at first. This one is difficult because it is at night.)

You can build your own missions in the FMB, but that's a whole other thread on how to use that............... But happy to help if you want to start using it.

Important: Make sure who ever is going to host, knows how and has done the port forwarding thing. Otherwise no one will be able to join your game.

Look here for info on how to port forward: http://portforward.com/english/routers/port_forwarding/
or get ahold of Alpha. He can help with this.