Step 1 - Finding the Mod IDs, name and version

1. Startup the game
2. Click "Workshop"
   
   
3. Download all the mods you want to use on your server.
   
   

4. Navigate to game files on your PC, default location is:
   %USERPROFILE%\Documents\My Games\ArmaReforger\addons

   In my case, it is: C:\Users\ServerHelp\Documents\My Games\ArmaReforger\addons\

5. Each folder is named by the mod ID, but to determine which mod corresponds to which mod ID you'll need to open the ServerData.json file inside the folder, it'll look something like this:
   
   {
   "id": "1234567890",
   "name": "Modname",
   "revision": {
   "version": "1.0.5",
   "dependencies": [],
   "scenarios": [],
   "downloaded": true
   }
   }​

    

   From that you can derive the mod ID "1234567890" , the mod name "Modname" and version "1.0.5"
   
   
   

6. Make note of all this information as we will need it in stage 2 (I recommend copying all the information into a text file you keep safe somewhere on your PC)

Stage 2 - Adding the mods to the server

1. Stop your server.
   
   
2. Click "Configuration Files"
   
   
3. Click "Text-Editor" next to "config.json"
   
   
4. Find the section:
   
   "mods": []​

    

5. Modify it as follows:
   
   "mods":[
   {
   "modId":"1234567890",
   "name":"Modname",
   "version":"1.0.5"
   },
   {
   "modId": "123456789",
   "name": "Modname",
   "version": "1.0.5"
   }
   ]

    

6. Save the file in the top left and startup your server.
   
   
7. Enjoy the mods!