ArmA: Armed Assault: Mission Editing
introduction to mission editing
The mission files are found in specific folders you will need to learn. Existing mission in .PBO format cannot be edited, only files in .sara and .intro format. However .PBO format can be modified to .sara and .intro formats using certain 3rd-party tools designed to recreate the original editable missions.
Missions will also contain .SQM format files which contain libraries of script functions. Available scripting commands can be found on these pages: