How to take different shots with my nikon d3100?

I want to explore my nikon d3100 i want to take different shots like make it dark a little make it green like nature something like that

Do you know how to use the cameras light meter?

You can adjust the exposure using the camera in the manual mode and use the shutter speed and lens aperture to over or underexpose your images

Since you've probably already taken time to read & study the Owner's Manual, watch this video tutorial for additional help with your D3100.
http://www.nikondigitutor.com/eng/d3100/index.html

It also sounds as though you need to learn about the Exposure Triangle which consists of ISO, Shutter Speed and Aperture.
http://www.digital-photography-school.com/learning-exposure-in-digital-photography

I had to chuckle at this: "… Make it green like nature… ". I promise you that unless your white balance is set incorrectly or your exposure is really off, if you take a picture of a green shrub or tree or any other green plant it will be green.