First, download Arma3Sync and install it. I have a download link here: Arma3Sync
Start up the program and begin by choosing a location to store your arma3 mods under the addon tabs.
Next, click on the repositories tab and add a repo.
Paste in the following autoconfiguration URL: http://repo.w83.games/autoconfig and click import, then ok. Connection information should populate automatically.
Select the fresh repo from the list and click on the configure button.
First, click on the download button (5) and then check for repo updates (6). This is how you will update your mod folder if the server updates theirs. Select all the @mods from the content list (7) and then click the download "play" button (8).
You can add the game server to your Arma3Sync favorites. This will allow you to launch the game directly into the server. IP address is 22.214.171.124 and port 2302
Make sure that the full modset is selected under the addon tab.
Select Battleye under the launcher options and check that you see the correct executable location on the bottom and a big list of mods on the right, then you should be all good to go!