Application server for dummies?

Question

Java

Are there any good materials on servers (application servers eg Wildfly, Webshpere)
with a good explanation of everything and everything? What ? Why do we need this or that property? Why is it configured this way? I only roughly understand what a server application, clustering is.
But I want to understand why and how to configure them (why the datasource is defined in the server configs, the differences between
standalone and standalnoe-ha, what other properties are declared there
and why.), all the subtleties and nuances. In a nutshell, my question is: are there any useful resources (preferably video materials)
for dummies regarding servers. Googled it, but basically they just come up with how to install an application server, how to deploy an app. etc.