Is replacing the spokes on bike wheels something you can learn to do yourself?
I'm a heavy guy and regularly have spokes break on my back wheel. Getting a bicycle repair guy to fix it is a pain in the ass and kind of pricey. Ideally I would like to have a couple of spokes lying around so I could fix the wheel myself.
I'm not a complete idiot with tools but I'm still very much an amateur. Can I learn to do it myself?
The bicycle repair guy trues it when he fixes it. How can I learn to true it myself?
And how do I know what spokes to buy?
Learning is basically trial and error with a guide. As for what spokes you want it's impossible to tell from afar, but there's quite a bit to look out for. Diameter, how it affixes to the hub, how many can be affixed to the hub, material, etc.
Seeing as I hate dealing with building wheels other than retightenig the occasional spoke, I'll point you towards the god of tinkering with bicycles, Sheldown Brown.. Some of the info is probably a bit out of date, but the general gist is there.
If you think this is a bit long, and I do think this, it might just not be for you. I think building or fixing wheels is the type of stuff where you look onto this mess of math and physics and either think this was made for me to nerd out or this sucks and I'll hate it. A new wheel honestly isn't that expensive, especially when you factor in how much time and material you're probably going to need learning it.
EDIT: This is under the assumption you have a rear derailleur and not internal gearing. Allthough in the later case I'd advise you to flog that one and buy a better one. The cheapest way to new wheels is usually to scout local used bike listings for something that'd fit and buy a whole bike, strip it for parts and use the wheels really.