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.