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

[Marabekm]

Ok first off, all versions of IL-2 will allow you to play co-operative mssions or dogfights. But everyone has to have same version as the guy hosting.

The co-op missions allows you to set up a fly a specific mission. And with co-ops you can have multiple people in the same plane. But once you get shot down, you can not respawn.

Alternatively you can create a dogfight mission and set home base for just one side and make all enemy flights AI. With this you can not share a plane with someone else. But if you get shot down you can respawn.

I recommend looking for missions at: www.mission4today.com this sight has plenty of missions and other goodies.

[majorfailure]

You might try DCG, third party campaign generator for il2.

It is very useful for playing longer campaigns vs. AI, you can influence the outcome of the battle quite a bit by playing well(or the other way round). It tracks losses in ground units an planes, and applies them to the next missions.
And has lots of options, e.g. worst weather to occur. And customizing campaigns is not that difficult, though creating your own full-blown campaign is a bit of work, but it is possible to do so(Want to play Japanese invasion of Hawaii -set up the campaign and have fun). Using it for years now, and still like it.

[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.