I started my path to electronics apprenticing for a tube amp tech and have come a long way in a year (my homework was amp building...)
Repair and builds are two different mindsets, but building is the better start.
Buy the book "The Guitar Amp Handbook" by Dave Hunter. Some guys here will dis it for valid reasons, but the first chapter completely walks you through a Tweed Princeton Circuit, which I think a beginner will really like.
Next pick out a good build amp. I am a mega fan of the 5f1 champ circuit. It's so Zen and makes a beautiful sounding amp every time. There is a great website of guys, lots just getting their feet wet, and many "been there" advisors. (Pm me if ya wanna know cause last time I mentioned, it was deleted).
Another book to buy is "A Desktop Reference of Hip Vintage Guitar Amps". The back is full of schematics and all the Fenders have a schematic and layout below, probably the easiest way to wrap your head around a schematic.
Learn resistor codes
Learn capacitor codes and conversions.
Draw the pinout for the tubes you will use (to drive it home)
Learn the difference between vintage and modern tube heater wiring.
Learn the difference between vintage and modern power ripple filtration values.
(This was a big post for me hope it doesn't go to waste
(I just built a D-U87 for 1/8th Neumann's cost, and am about to make the famous compressor clones. Building will save you serious $, but be warned it is addictive...)