Tony R. Kuphaldt's Lessons In Electric Circuits is a free set of texts. Although sections of some of the later volumes are incomplete, the first two volumes dealing with DC and AC give good introductions along with safety information and references to external sources. Because the series uses SPICE (a circuit simulator), you will be in a better position to use other resources like the electrical engineering courses offered by organizations like edX (circuit simulation is common).

Hi,

This is also a good even if a bit old site regarding the subject:https://www.repairfaq.org/sam/sammenu.htm

Obviously read the safety notes on the page before beginning, and the extra safety notes and disclaimers on the sub-pages related to specific kind of equipment.

MagefromAntares wrote on Today, 09:37:

https://www.repairfaq.org/sam/sammenu.htm

100%, I too grew up with Sam's guides 😀

You should also know the theory of operation for whatever you're working on - for example, "a typical PC does not need memory, storage, any expansion card or external accessory to turn on and possibly even beep", so you can then deduce a possible test for "it just turns off immediately"; of course some exceptions will defy common practice... 😀
Sam indirectly said the same thing: even if you don't manage to fix it - or don't get confident to do the job in the first place - you'll hopefully still come out better in knowledge and experience!

And of course you'll have to define "electronics", "device", and "repair": compare a classic tube TV where component-level servicing is the norm, a PC where that would be exceptionally uncommon, and a car where it totally depends on which subsystem someone is after AND who that person is! While Arduino and Raspberry have greatly blurred the boundary between "electronics" and "computing (since give or take USB became mainstream)" 😀

Solder practice kits.
Get a decent soldering iron and see if you can do it first, should cost £50.
Then move on from there.
You need to walk before you can run.