White Balance, or rather, Correcting White Balance is the process of removing the color cast, so that your photos Look Right to the eye. Sometimes, when we use a type of light, the photo can look blue, yellow, or odd...
This is most likely, because the color temperature of the light shining on your photo was different than the camera was 'expecting.' In post processing, we can fix this, by telling the computer, that areas in the photo are true white. Our brains are pretty good at seeing an area of white and ID'ing it as white. Cameras, and their pesky computer brains are not quite as forgiving. They capture exactly what they've been told to, to the best of their ability. (A lot less ability than our eyes/brains can handle and process!!!)
This graphic, (below, from FilmMakerIQ) shows the apparent temperature that certain sources of light appear to be:
Color Temperature is tricky. Basically, our minds perceive a true white as about a 5000K - 5500K light source, which is a Mid Day Sun. Most decent flashes try to be between 5000K and 5500K. Anything less than 5500K is perceived as 'warmer orange'. Candles, Sunrise, Tungsten and Incandescent lights. Anything burning hotter than 5500K, is perceived as 'cooler blue', like cloudy daylight, shade, 'moonlight led's' some Actinic Lighting.
Most of us have Photoshop or Lightroom for post processing. The software has a setting for Adjusting the Lighting. Using your software, you can click on an area of true white, and tell the camera that this is white. In the same, Adjust Lighting you can also use your eyedropper tool to adjust the true black, as well as grey point.
Most of our cameras have some Preset White Balance settings. Understand these basic settings and you are on your way to better photos. You don't need to memorize the numbers, but you really should understand the concepts. Cool, daylight, warm, etc. Capturing Light is the only way we can get photos into our cameras. Understanding how to control and capture that light will make us all better photographers.