WTF? Why the **** do they send 11Bs to Troops and stick me in an HHC?
Anyway. Are you on a Bradly? If so you are going to need to learn the track (something I know nothing about so I can't really help you).
If you are on a truck you will need to learn how to operate and maintain your weapon (should be obvious but you asked), I'll assume it's going to be a 240 or .50. From my experience with 11serise guys I'll assume you don't really know the .50 or MK19 but neither are difficult to master. If you have a MK19 be nice to it and make sure that everything is nice and smooth and well maintained at all times (no burs or **** to catch on the ammo during the feeding cycle) as a jam on that weapon is a pain in the ****ing ***. But yea, 240, .50, MK19... shouldn't be an issue.
If you are on a Stryker you may have to learn the CROW system (should be sent to an official class on it)... or if you are on one of those crazy variants then whatever it is you have on top of your truck (I call them trucks because they have wheels).
Your driver will take care of most of the vehicle maintenance but there isn't any reason you can't help out.
You need to know your radios, how to fill them, work them, trouble shoot them. You need to know what antenna goes to what radio, where the antenna wires are routed, if you have one or two power amps and what radio is powered (if you only have one) so you know what radio to use for PLT and what to use for Troop comms.
Being a gunner can be bad ***... I had a lot of fun as a gunner. Just make sure you know your radios and your weapon system. If you have a good driver and TC then you don't have much to worry about it. Think of it as "your turret" and set it up so it so it works for you. Scrounge some ammo cans for extra mags/ smoke/ grenades/ clp/ VS-17 panel and bungee cord them up there with you. Make sure you have a 9-line taped up there. If the TC goes down it's on you to fight the truck.
As far as "cav operations" in my experience we are either used as PSD or just like wheeled infantry. The "big war" stuff we are supposed to do doesn't really come into play.... much to my
I hope that helped... if you have more/ more specific questions let me know. I'm not the only 19D around but lets face it... I'm badass