Jill gave some excellent advice in response #1 to your question.
You need to learn the relationship of shutter speed, aperture and ISO and how they relate to properly exposed images. If you set your D7000 on Auto it will select proper aperture, shutter speed and ISO.
You should purchase a beginner's book on exposure and/or take a fundamentals class on exposure. There is probably a lot of good info on the internet regarding fundamentals of exposure. Once you realize the relationships of the 3 (aperature, shutter speed and ISO) you'll be off and running.