Roppers Academy Computing Fundamentals
This is the flagship course of the Ropeprs Academy site. Even if this stuff is the fundamentals there is rarely a reason you would have to learn them in your day job.
Complete the sections here which cover Hardware, Operating Systems, Windows Internals, and Linux Internals.
Message @Dennis Devey to tell him you are starting the course, and then use the #training chatroom for any questions or discussions.
This will take a long time, but you will learn a huge amount.