Good advice RT,
Not that you need any of the following crchisholm, but if others view this topic it may be helpful to them. The things I see that makes it tough for some are listed below.
I would add that being able to at least read Gcode and understand what it is telling the machine to do (even if you have to use a reference manual to translate it) really is not an option. Many think because they have CAM software that will generate Gcode they can skip this bit. Nothing could be further from the truth unless you have someone to train you in defined instances/ work flows. Not understanding Gcode and having CAM software is the same as having a calculator and not understanding math.
Understanding electronics, or anything electrical is a big plus. If you understand how your hardware works, what happens when you send X volts to pin X of X component has X effect or does X then the rest of it comes much, much easier. A ryme I made up years ago.......
It all boils down to IO
Some high, some low
Some fast, some slow
It all boils down to IO
With any type of automation, controller, PLC, CNC,etc. (even a simple relay) all any of them can do is receive inputs, do some magic using those inputs and send outputs. This is all it is at its foundation.
The only thing any software can do is change bits of data, 1s to 0s and 0s to 1s. You have to use hardware to convert the 1s and 0s to anything we would find useful in the outside world (like voltage) and convert things we find useful to 1s and 0s (the only thing the software understands). Some hardware will receive input signals and convert those signals to data and send that data to the control. Other hardware will receive data output from the control and convert the data into useful output signals. Some hardware will do both.
Understanding how the hardware you are using works to some degree is mandatory. To what degree you will need to understand it depends on what you are doing but it is impossible to know too much about it and very easy to know to little. Read your hardware's documentation and if some things don't make sense google the word, phrase, etc., talk to friends about it, read books on the topic, search and/or ask on this and other forums etc. until it does make sense. Once you understand how the hardware works, what makes it tick...... controlling it is pretty straight forward.