After downloading the mod, use a program such as 7zip or WinRAR to extract the main folder of the mod.
Navigate to assets/mod_overrides. The assets folder is supposed to be in your game's installation folder (don't know where that is? click here). Create the folder if necessary
Move the main folder of the mod from step 1 to the folder you navigated to in step 2.
CAFCW is needed for Custom Attachment support, such as optics.
Weapon Painter is needed to access the Getingbrigad 20 Round Mag variant. I personally have no clue what it is a reference to, it was just a request by Nya.