ELI5 swapping pickups

I’ve been toying with the idea of upgrading pickups and unfortunately when it comes to my guitars i’m a very diy kinda guy. After looking around i keep seeing things i know absolutely nothing and instead of scrolling through articles and forums for a few hours I was hoping someone more knowledgeable than me could give me a quick rundown or point me towards quality resources.

I guess to sum up my essential question, when looking to swap out pickups, what do I need to know as far as wiring/electronics? Obviously i know the new pups need to fit in the pick guard and cavity and all has to be shielded properly, but what do i need to know about resistance, inductance, etc? Whats important or negligible, what effects compatibility, tone, yadayada. Also besides a obvious a soldering iron, are there any tools i should look into investing in? Multimeters or something?

I apologize if these are simple/ tedious questions, i have no proper experience with this sort of stuff so its all just a little foreign to me. Thank gang <3