Understading the different server cache types and techniques


I am new here and would first like to say thanks for this site :slight_smile:

These last days I was into understanding server side caching, especially with Wordpress/PHP.

I read there are different types:

Database Cache
Opcode Cache
Object Cache
Page Cache

My websites are hosted on Litespeed servers, I use the LSCache WP plugin with it.

The Litespeed staff told me that I can also add object caching with this plugin, there are options like Memcache and Redis.

My question is what is what and how does it works?

I’ve read page caching is about caching the HTML.
Memcache and Redis object caching so that is ment to cache the data base, so also images etc. so I guess besides the HTML file, not?

Maybe someone has good ressource like with good schamata?
I know the basics of PHP I wanted to add here.

I’ve also read about a technology called Varnish, Railgun from Cloudflare for exemple.

Kind regards