Config is the heart of your addon, no matter how nice model and textures you have, they are empty shell without a configuration to make it all run in-game.
Config basics and Configs in general to get you started.
CfgMods to identify your mod. Also mod.cpp in mod directory.
Dispersion for weapons.
Pilot proxy rtm file creation.
Custom face, how to add custom face to your soldier.
Shotgun config for real shotguns.
(<class>) not found in active addons error, how to fix it.
Extract original bis configs as text files to be used as reference.
Vehicle sound tutorial by realitymod.com