Bike ignorance I admit. What is the purpose of a headset? Is it used to raise the bars?

Apologize for the dumb question. I ran across something about Chris King headset and just don't have any idea what they are used for, or why someone would replace one, etc.

The headset is the bearing set that lets the fork turn in the bike's frame so you can steer. Chris King makes high-end ones, often found on custom-built bikes where people specify each individual part of the bike to their liking.

A good place to refer to when you have questions like these is Sheldon Brown's site:
https://www.sheldonbrown.com/
For this question the answer appears at
https://www.sheldonbrown.com/gloss_ha-i.html#headset

Sheldon my have passed, but his site is still a treasure trove of well-organized, easily understood information.