AC is earned in all game modes, except combat patrol.
You earn AC for completing certain tasks within the game. For example you earn 100 AC for killing an enemy. You also earn AC linking nodes in LINK or capturing flags in CLASH.
I believe (but could be wrong) that the AC and XP you earn throughout the game is only rewarded to you if you complete all rounds of the current game. But I might be wrong.
As stated two posts up in this thread, the Editor is very much similar to the ArmA 3 editor. There is a TON of videos explaining the ArmA 3 editor on youtube. There is even a wiki, on which there is information useful in scripting :)