I also agree a good place to start for a beginner is (P)rogram mode. You can always adjust both aperture and shutter speed in (P) mode to experiment, as well as exposure compensation. As you get more confidence with setting exposure, many photographers graduate to (A)perture mode, where you can control depth of field more readily than in (P) mode. The disadvantage of (P) mode is that it often sets exposure settings with the lens wide open, which is not always the way to get the sharpest images.
Your have been given lots of good suggestions about reading. I'll also emphasize that the most important thing to learn is setting exposure. Even with excellent matrix metering in Nikon cameras, you have to always be thinking about subject exposure and you can tweak that with the compensation dial.