White balance is the ability to change the temperature in your photo, taking into account your light source.
If you ever wonder why your picture turned out yellow, the snow looks gray not white, the temperature turned out too cool and not warm enough...those are all due to the incorrect white balance setting.
Most cameras have the ability to change the white balance. They have pictures that represent light sources. If your light source is the sun and you are outside put your setting on the picture of the sun. If you are taking a picture in the shade place it on the picture representing shade. You also set your white balance on auto and change it during the editing process if need be. Lightroom is great for changing your white balance.
Sometimes I find that I like the temperature of a completely different setting. So don't be afraid to play with it!
Here are a few examples of the same picture but different white balance settings.
I'll have another post on how to set your white balance manually soon!