videos and such are nice but there are so many different things that can go wrong, it is a matter of experience to see them all and learn what symptoms point to what. see if someone local (a shop preferably) has some room to let you hang out and learn. troubleshooting is tricky depending on the problems and hands on is the best way to learn. i started a long time ago and would be presented with a problem and then research a ton online to see what the issue might be and then to try and fix it. over the years i have to look up less and less but it took a long while to get that far.
as for buildign one, simply building a couple is enough to be good at it
very easy to put the pieces together and little place to make an mistakes.