ArmA 2 / ArmA 2 Operation Arrowhead main editing page. A lot of ArmA editing is compatible with ArmA 2, if you cant find something in this page, please search from ArmA pages too.
Beginner Editing Guide if you are total newbie, read this to get basic understanding.
Gnat video tutorials on youtube. Install ArmA 2 editing tools and four videos of Oxygen 2 use.
Hand Anims, Weapon holding animation etc.
Custom Artillery how to make it (not sure).
Signatures for your PBO files.