Hi Aegos,
The Few Good Men is predominetly a community focused on the Combat Mission series. You'll see in the various forums the different game versions etc. Our ARMA III activity is a smaller group of mature players who enjoy the mil sim and usually meet up on a Sunday. You'll find a lot of posts in the ARMA III section about ops, game play, after action reports and about the mechanics of using mods etc.
For ARMA mods most prefer to use a piece of shareware software called playeithsix, as Nelson mentions. The website is
http://play.withsix.com/. One doesn't have to, but it is perhaps an easier place to start as one progresses along the learning curve.
With this software you can download the various mods we use based upon the description name, e.g. @A3MP. You don't need to know exactly what they do at this stage, just ensure you have them all downloaded based upon the mission brief. The 'optional' are also recommended as they argument ones game play. Use of any additional mods than those listed is not posdible as the server will not connect.
Keep an eye on the ARMA III forum section, I'll be posting about the next op in the coming days. It helps if you says if you can join, I can then ensure their are enough slots and PM you the server password.