Heck, I don't know. I've always used "Nikkor" and "Nikon" interchangeably when talking about the lenses. If you want to read up on the various Nikkor/Nikon lenses available, take a look at this page -> http://www.kenrockwell.com/nikon/nikkor.htm
Flash mode is pretty much what it sounds like: Using a flash during taking photographs. Generally the shutter speed is fixed, so you have to adjust the exposure via the aperture size. This is pretty much handled automatically by the camera these days, though, so you really don't have to think about it too much.
One term you should become INTIMATELY familiar with if you plan to shoot closeup photos is "depth of field". Knowing how best to work with this topic will make or break your photographs. With closeups, the widest depth of field you can get is what you want. That means small aperture, which in return means more light needed to compensate for the slower shutter speed the small aperture forces for a proper exposure. Which is where flashes come into play. Good closeups with good depth of field just need lots of light.
The good thing about digital cameras is that experimentation to learn your camera won't cost you an arm and a leg in film developing. Plus you can get immediate feedback to the setting you are experimenting with. When you think about it, compared to 35mm cameras, the new digital revolution in cameras is actually saving you money, no matter how much you spend on your gear. The money you save on film and processing that you would have had to spend with a 35mm is FAR more than your digital camera costs you.
Have fun!
