Oh, I'm sure you're bright enough, Joe, never fear. After all I manage to do it, and if I can, you surely can.
It does seem confusing at first, which is why I recommend (in all my newbeeness) to read through the Newbee Guide a couple of times before you get started, but in short, the OG is the original gravity, before you pitch the yeast. You really need that so you know how your mead is progressing, as it drops as sugar is converted to alcohol (which is less dense). You need to pay attention to the gravity as the days pass, because you're looking for the 1/3 sugar break (when one third of the sugar has been converted to alcohol) and the 2/3 sugar break (yep, when two thirds of the sugar has been converted to alcohol) to monitor the fermentation process.
You calculate those breaks by taking the amount of sugar over 1 (in a 1.100 must that would be 100) and divide it by 3 (which would make the 1/3 break at around 33 and the 2/3 break around 66). The problem with not doing the OG is that you can't easily calculate those breaks otherwise (Aaron's trick with the scale notwithstanding) and since they tell you when to stir and feed, they're rather important.
Generally you aerate only to the 1/3 break, and depending on what kind of a must you have going you feed at least then, and probably at the 2/3 break as well.
SG just stands for Specific Gravity, which is a ratio of the density of the must when compared to water. FG is the ending gravity, which can be pretty well predicted by plugging the sugars into the mead calculator, but you can measure it with the hydrometer too. It's fun to see how close you get to your calculations, and once you have the OG and the FG to put the numbers into
this calculator to see what your ABV is.
But another piece of advice I can give you that served me well was to read MANY recipes similar to the one I was thinking of trying. That has kept me from screwing up too too badly and I haven't mucked any batch up too badly to drink. Yet. I don't think.
;D