It is important to understand that different light sources of very often different colors. For instance (relative to daylight which is considered white), incandescent light is orange, cangles are red, and shadows are blue. Our brains can automatically adjust to the different colors of light so that you can read under candlelight and your brain will consider the paper white, but you digital camera may need to be configured to do this properly.
In the old days of videography, the camera operator would use a white piece of paper to calibrarte the video camera to the color of the light in the room. This process was called "White Balance". Our digital cameras are similar to video cameras and need to "white balance" to the light in the room too. This is now done automatically in the camera, and in most cases you'll want to leave your camera on Auto White Balance mode. However, you will run into special cases where the light in the scene either is so far off that you want to force the white balance to have more effect, or you want to force the white balance to have less effect that the Auto white balance does by default.