White balance (WB) is a global adjustment of the intensity of the colors. The aim is to render the colors, particularly the neutral colors (such as gray and white), correctly.
The auto WB gives you excellent results in most situations. The Automatic shooting mode and most of the Scenes shooting modes use the auto WB setting.
The Creative shooting mode offers some different WB presets. With those presets you can get very consistent results in certain lighting conditions. WB presets offer you the possibility to get some special colour effects, for example, either a yellowish or bluish tone, into the photos depending on the setting and lighting conditions. You can get a heavy boost on the blue tones by using the incandescent WB setting on early morning landscape photos just when the sun is about to rise. Or, you can get a nice boost on the yellow, orange, and red tones by using the sunny WB setting on the sunset photos. In the sunset case, auto WB might wash out the colours too much, as it targets to find the white point in the photo.
To change the white balance setting, make sure you are in the Creative shooting mode, then select the white balance icon on the left and a setting.