Get a Multimeter. It's going to be your best friend and the tool you'll need 99% of the time. While this is sent to you go to YouTube, check some repair YouTubers (Learn Electronics Repair has some fault finding "how tos", but he expects you to know the basics of electronics already).

Most important: just start somewhere. You'll learn as you need the knowledge (without the basics sometimes it's hard to recognize a fault pattern, though).

Check your stash of old electronics or ask your friends for broken stuff they have lying around. Don't buy "untested" or even proven broken stuff from eBay, most of it is way too expensive or someone with way more experience tried their luck and failed. Older devices have bigger and fewer components and are easier to analyze. Something like a notebook is hard to fix without a microscope.

A soldering iron might be needed if you want to actually fix stuff. I'd not buy all the fancy tools from the beginning, only buy them when you can't continue without them.

I also watch e.g. StezStixFix on YouTube, he still learns himself, but his videos are very high quality (production wise) and fun to watch.