If you are looking to a group that uses private mods, they will always provide clear installation instructions. If you are looking to create a private mod, start by learning the Arma 3 Tools (Terrain Builder, Addon Builder, PBO Manager) and set up a private repository using Swifty or Arma3Sync.

The Arma community is unique; it is built on the back of free user-generated content. The idea of hiding that content seems antithetical to the community’s roots. However, for many developers, going private is a matter of necessity and pride.