Setup: ARMA3

Copy the ws_fnc/ folder to your mission's root directory. The follow step depends on whether you already have a description.ext in your mission's root folder or not.

No description.ext

Simply copy the description.ext from the ws_fnc/ folder to your mission's root directory.

Existing description.ext

Open your description.ext in a text-editor and check if the line cfgFunctions already exists.

cfgFunctions not present

Paste the following to the very end of your description.ext:
class CfgFunctions {#include "ws_fnc\config.hpp"};

cfgFunctions present

Paste the following righter under the first { but before any other class:
#include "ws_fnc\config.hpp"

Example: F3

If you are using F3, your cfgFunctions section would look like this:

class CfgFunctions {
#include "ws_fnc\config.hpp"
class F  
  {  
  //All F3 relevant functions  
  };
};

Troubleshooting

Any errors in the description.ext will cause ARMA to crash to desktop. If this happens make sure there are no superfluous bracket or duplicate definitions.