Much of the ArmA mission making is same as in OFP, so you should refer to the OFP Missions area for details. However here are the ArmA specific stuff.

• BIS class names

The default BIS class names for all units and vehicles.

• Campaigns

Campaign information.

• Music track names

All default music tracks listed.

• Eventhandlers

List of EventHandler's.

• TeamSwitch

How does the teamswitch work, what commands are available.

• Misc stuff

Misc mission editing related.

• Intro tutorial

Quick tutorial for making intros to missions.

• Cutscene tutorial

Cutscene tutorial, how to create cutscenes using SQF scripting.