You have got to start at the basics and build up from there. Cleaning the bike, adjusting the brakes, changing the brake blocks, changing tyres and punctures, the list goes on......trial and error. I started with cycling at 10yrs old with my first bike from the local tip in 1970 and it has been a passion of mine ever since. Starting with basic tools and building up from there. A few years ago I built my own SWB recumbent from scratch from old bikes and learnt how to weld.
It can turn into an obsession. I have invested a decent lump of money in tools and equiptment so I can do anything on the bike. You have got to study every angle and dimension if you go into it deeper. It's not rocket science but you need to be hands on and get a feel for it. I have broken into wheel building now which I find gives me great satisfaction in doing. I will never go back to buying wheels off the peg as I can hunt the parts cheap and build them myself. The more you get familiar with how things work, the easier things become. You have got to look at this way, If you broke down with a puncture 10 or 15 miles away from home, Can you fix it? Building a bike from scratch ? that depends on you, tools, experience and knowledge.....It can be rewarding