Step 1 - Download
Download ArmA3Sync here. Press the download button inside the red box and execute the file in order to install the app.
Step 2 - Locate the .exe
After the installation, click on the shortcut on your desktop in order to run the app. There will be an initial prompt to tell the path of your arma3_x64.exe, which is located in your ArmA III folder, e.g.:
C:\Program Files\Steam\SteamApps\common\Arma 3\arma3_x64.exe
Make sure to choose the arma3_64.exe itself, not only the folder that contains it.
Step 3 - Configuration
Arma3Sync is now ready to be configured. On the left hand side, you can see the mods in your ArmA3 folder which are currently installed and available. On the right hand side are your configured modsets ready to be used. At the moment, there are no modsets set up, the game would launch without mods. More about that later. For now, switch to the tab called Launcher Options. You can basically pick what you want, here is an example.
Step 4 - Add the repository
Navigate to the Repositories tab and press the button Add repository. Fill in the following:
|Public auto-config url||https://ironyworld.de/arma3/repo/.a3s/autoconfig|
|Repository name||Your choice (e.g. Ironyworld repo)|
Press OK to close the window.
Step 5 - Synchronize the repository
Tick Notify to get update notifications as soon as the Ironyworld Repository has an update available. Press on the button Connect to repository and check if there are any mods available for download. If thats the case, select the ones you want to download and press the Download button. This might take a while.
Step 6 - Activate repository addons
In the Addons tab, press the button named Modsets, where you can conveniently pick all the mods belonging to a repository. Pick the one you just created and press OK. Now you've created a group of mods, but you haven't activated them yet. To do that, just tick the tickbox.
Step 7 - To battle!
Finished! You can now play the game with the button Start Game in the bottom right corner. From now on, you'll have to always start the game with ArmA3Sync or else the correct start parameters won't be set. Have fun!