Greetings fellow ArmAholics. I have created a series of tutorials going over everything you should need to know to build a simple-moderate level missions from the ground up in ArmA 3. The ArmA editor is very simple to understand and use once you get to know it, but starting out it can be a little daunting.
Building a Simple Mission Part 1 - Editor Familiarization and Friendly Spawn Setup
Building a Simple Mission Part 2 - Garrisoning an Enemy Base
Watch a playthrough of the mission created with just the two tutorials above
Editor Tutorial 2 - Building a Custom Gearbox
Editor Tutorial 3 - Markers, Waypoints, Triggers and Syncing - Whoops, I screwed something up in this video, check this link to see what it was and how to fix it.
Editor Tutorial 4 - Module - Sites
Editor Tutorial 5 - Modules - Support
Editor Tutorial 6 - Custom Unit Loadouts
Editor Tutorial 7 - Modules - Tasks
Editor Tutorial 8 - Modules - Briefings
Editor Tutorial 9 - IEDs and Ambushes
Editor Tutorial 10 - AI Building Patrols
Editor Tutorial 11 - Multiple Trigger Conditions
-Editor Tutorial 12 - Building Custom Bases
I hope this helps you who are new to editing, and maybe even show some of you that are more experienced a trick or two!