Short: It pre-stores a ready-made version of your page, so the visitor doesn't have to load everything from scratch every time, but gets the faster "pre-cooked" version.
More specifically: The essence of caching is that the server or browser temporarily stores a pre-prepared copy of the page. This way, when someone opens the website, they don't have to re-process all the images, styles, and code, but instead load the faster, "ready-made" version. This significantly reduces loading time and also improves the user experience.
