Welcome to the forum.
You are where I was 6 years ago. I started off with a Canon Rebel XS with one zoom lens 28-80 and later a sigma telephoto zoom. I largely taught myself and was not afraid to ask questions, you learn a lot online, also there are continuing education courses everywhere in Photography, I only wish my schedule was flexible enough to leverage them.
Today is different, I use mostly old gear from the 1960's and 1970's and I love the totally mechanical as opposed to electronic process, along the way collected most of the SLR's that mattered from that time period. A dangerous addiction
"Life moves pretty fast, if you don't stop and look around once and a while, you might just miss it."
I am a lot closer to being where you are now than most of the people here, hehehehe so maybe I can be helpful in relating to a beginner (which I consider myself to be not far from).
One thing that I found to be a useful analogy expands on what mhv said (or rather draws a parallel): pouring light onto a light sensitive material is exactly what you are doing, but to understand it more easily, think of a proper exposure as glass full of water. In order to get the rigth exposure, you need the glass to be exactly full - not quite full, and you have dark, underexposed pictures (thin negs), spill some over, and you have overexposed, blown out pictures (dense, black negs). Now, you have two ways to control the amount of water (since God has the tap in hand): how long you let it run, and how big a hole you let it in through. So, picture a waterfall, and you have a cup in your hand that you have to fill just right. You have a cover over the top that lets you adjust the opening size (hey, thats apperture!), and you have the say over how long the cup can be "exposed" to the stream of water (the shutter!). As you can imagine, you can get the same amount of water in there by letting it run twice as long or by letting it run through a hole twice as big! Pretty simple, right? Now - your meter tells you how much water is running - is it a trickle (dusk, cloudy morning, etc) or a flood (sunny afternoon, snow, etc).
Having said that, you have to grasp what it is the meter is telling you. Contrary to what most people think, a reflective meter (the kind in your camera - it measures light reflecting from, rather than falling on, the object of your attention) can't think for itself, and measures one thing: 18%, or as its often called middle gray (no idea what its in the middle of). The idea is, if you took a picture of that exact colour, it would look exactly that same gray in a final print if you did everything properly (albeit not necessarily very creatively). If for example, you took a picture of a patch of snow according to the reading, it would come out exactly gray on your picture. If you took a picture of something perfectly black, it too, would be gray. To sum it up - if you had a perfectly black wall, and a perfectly white wall, and you took a shot of both exactly as the meter tells you to they would both look... exactly the same in your photo. Most scenes have a variety of tones, so you get highlights, and shadows - so you get a pretty good picture most of the time. But, until you understand this principle, you will have some very dissappointing pictures.
This final part is something that may be met with various responses. I am by NO means suggesting that what you need in order to learn is different equipment, but... I find that modern full-auto SLR's have so many features, and so much possible automation and endless combinations of auto this and manual that and so on and so forth... that I think you may find an old fashioned camera a better learning tool. They are dirt cheap, dead-nails reliable and never leave you guessing - if you screwed up, you screwed up - no guessing if perhaps special function x was turned on and you forgot to disable auto-whatchamacallit, or perhaps selected this option or that one... NO. You have at best a meter, a shutter speed wheel and an apperture ring. A lot easier to learn the relationship between those when its all that you can directly affect. And many of these cameras come with wonderful glass that will match your Nikon in every way, or at least for all practical purposes. I saw a Pentax and a Minolta like that right here on APUG for less than $50. And since they are on the bottom of their depreciation curve, hey - when you sell them, they will still be... yep - you guessed it, about $50 I just think they make learning easier by removing distractions, guesswork, and all extrenous features that you probably don't need yet and don't know how to properly utilize.
Like I said - I count myself in the ranks of the (perhaps) advanced beginners, so my advice is what it is - but you are very welcome to PM me with any questions. If I don't know (very likely), I will probably be able to point you to someone who does.
Best of luck, and like someone said - first and foremost - go out and shoot like mad!