I'm installing a debian server.
The server needs a specific version of java, so I'm installing from the self-extracting file.
But I'm new to the linux world and I want to put the jre in a place that will make sense to me when i'm better acquainted with the folder structure. where should I put it?
You could install it under /opt. That would keep it separate from the system directories where a Debian supplied version of Java might be installed.
Yes /opt would also allow you to be more aware of what is interacting with it and avoid any unintentional upgrades or alterations to the installation.
This is how we layout out sdk's
and so on.