Can you describe in more simple terms how Varnish works?

Question

Varnish

In response to a question about servers, I received the following link.
Varnish
, as I understand it, is engaged in this application for caching and, judging by what they write on the Internet, it copes with this very well. Here's the only question that's bothering me. If it caches, then where, in RAM? If yes, how much RAM do you need? How to roughly calculate

Answer 1

If it caches, then where, in RAM?

Varnish has such a thing as "storage backend", i.e. storage. Available on disk, available in RAM.
Restrictions are set in the settings, they recommend up to 75% of free RAM.
Like any other cache: number of objects * size of objects