So, I know I'm about to flaunt my ignorance, again, but I need someone to tell me what this is, and what it does.
I'd look up the function myself, if I only knew what that little ring is called. There have been a couple of times where I inadvertently clicked the minuscule tab, unlocking it, and then inadvertently moving the aperture from the 22 to something else. It effectively incapacitated any function whatsoever.
It's your aperture ring. G lenses lack it (G is for Gelded), non-G lenses have it.
They are useful at times- Notably if you want to get crazy with lens swapping mid shot during long exposures, but they are more reasonably useful during Macro photography if you do any lens reversing, as you can very easily and accurately stop down your lens when it isn't connected.
That's what I've used them for, anyway. Otherwise I just leave it locked.
ETA: It doesn't incapacitate the camera with all lenses. Older lenses require that you use the aperture ring to manually set your aperture and thus they function in all modes normally, and in fact lack the lock tab that you'll find on newer lenses. It's actually kinda fun to use the old school rings for a reminder of how things have progressed. The aperture ring was something that was used pretty ubiquitously on all sorts of cameras back in the day, not just Nikons. They've just kept them intact on some of the modern designs.
Aperture ring can be VERY useful for video shoots, that's why Samyang has a new kind of video lenses (that can be used for photos as well) with a fluid aperture ring.
