As the term suggests, it is for color calibrating, specifically using the color white. To calibrate your white balance, you need a white card. You can also use an 18% grey card.
The simplest way to get a white card is to use a sheet of paper. If you want something that will last and you can bring to all your shoots, you can use a laminate sample or a piece of plastic. If you have a clapperboard, you can just use the back for white balance. These cards are made for it. These cards add a target for focus. And this is a very popular foldable “card” with a target.
If you’re looking for how to set the white balance in your camera, you may need to refer to the user manual. For a lot of cameras now-a-days, there is probably a dedicated button for it. On my Panasonic LUMIX DMC-G85, I just press the WB button and select on of the custom options. Hold the white card in front of the camera and hit set.
X-rite makes color charts that are used for color correction. They can be useful for white balance, especially on footage that is messed up and needs to be corrected in post. The X-rite ColorChecker Passport is a small color chart with a color swatch grid, white, 18% grey, and black bars, as well as a radial design for focus. Because of this, this is the only thing you need for white balance and color grading. If you are not looking to do color grading, get one of the cheaper options listed above.
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