I'm guessing you are using automatic mode on your camera, and using a white or very light background. In auto mode, the camera is designed to produce a picture which is overall a shade of grey, which is what a "normal" scene would generally be. There are several ways to compensate for that, but you will have to get out the users manual, and learn how to use some of the other functions. The easiest would be using "Aperture Priority", which should appear as an "A" on your dial. Set the aperture to 8, the camera will set the shutter speed, which will be too fast, because it's still trying to turn the scene gray, assuming you are using a white or very light gray background. So compensate for that by setting the shutter speed down by a few steps until you get the proper exposure. Using an aperture of 8 or greater will give you greater depth of field, which is the area in which your subject remains in focus, but will require longer shutter speeds. I hope you have a tripod, if not, you will need one.
You will want to do some reading, and become familiar with camera speak, such as "aperture, f-stops, shutter speed, exposure". These are the keys to the kingdom to better photography. It's really simple once you understand the jargon and the way exposure works. Exposure is simply a matter of balancing the aprerture(how wide the lens opens, expressed in f-stops), with shutter speed, which controls how long the sensor is exposed to the light entering the camera.
When the lens is open wide [f 2.8], you need a faster shutter speed, and you ;have less depth of field. Conversely, when the lens is "stopped down" [f 32] you need a much longer shutter speed to allow the same amount of light through the lens, but have a much greater depth of field.
Dan