[Plugin: WP Super Cache] How does Wp-Super-Cache work?

This is a plugin that most wordpress sites seem to use so I was hoping someone can answer a few questions I have about it. I want to know how caching works. I understand that a cached page is static html as opposed to a dynamic page that makes calls to the database each time it is requested. But I don’t understand how the caching happens.

Does Wp-Super Cache, cache a page only when someone has visited the page once and keeps that page cached until the expiry time is over?

If the above, then is the page cached only for that person or for everyone who visits the site since?

Or does Wp-Super Cache, cache all the pages on a website simultaneously (irregardless of whether a human has visited that page or not) and performs this task again when the expiry time is over?

When I enable super cache on my site (with compression) it seems to be fast only when I go to a page and load that page again. If I go to a page for the first time, it takes the usual amount of time.

Also, even if I go to a page multiple times, in another browser the same page it loaded at normal (non cached) speed.

Thanks.

https://www.ads-software.com/extend/plugins/wp-super-cache/