Xender

Hello, im too interest in moding arma, but i don't know how to start it. (Im game dev student so im able to make something :P). I have few questions: 1) Mods like DayZ is written as mission file or it a code written outisde a game? For example, bandages, blood bags, zombies etc it's all scripts written in mission editor and connected with assets or it's something more? 2) How to start wrtting mod or new features, from mission editor or as external files source files?