Different kinds of light have different color “temperatures”. Color temperature is measured in "degrees Kelvin." The color temperatures in the scene you are photographing will affect how the colors in your photograph will look. To get the correct colors, the camera allows you to choose a “white balance” and will add either cool or warm hue to balance the color temperature of the scene.
It isn't necessary to memorize Kelvin temperatures unless you want to be very specific with the Kelvin setting on your camera. If you'd like to learn more about that, let me know and I can share some resources with you. For most of us though, understanding the white balance setting on the camera will be enough and many cameras do very well on auto white balance, unless the scene has multiple, different light sources, in which case it can get a little confused.
Most DSLRs have the following settings for white balance:
The camera is adding different hues of color to counter the color of the scene.
Here are a couple of examples: I created two different images of the same scene by only adjusting the white balance setting. The image on the top was created using fluorescent white balance. The image on the bottom was created using tungsten white balance.
In reality I was outdoors on a cloudy day but by asking the camera to add purple (florescent compensation) or blue (tungsten compensation) to the scene, I was able to create something a little more interesting than a picture of carved stone on a cloudy day and the blue, I felt, was a better capture of the mood of the location.
The following exercises will help you get a feel for your white balance settings:
TIP: if you want to enhance the colors of a beautiful sunset, you might consider shade or cloudy, as it will increase the warmth in the scene.