for me it all started with my bikes as a kid, flat tire, hell ill fix that. then went on to mini bikes, and go carts, blew a lot of small engines up, like rods blew threw the blocks lol good times.
then when i got a car, my parents told me flat out, and i quote: " do not ask for a dime for gas, insurance, repairs, tires ect" so with those words being said i had to do my own repairs. got lots of used parts from the junk yard too. best way to learn is on a car you dont care about, aka junk yard car. do all you screw ups removing the part you want, so you learn the easy way to get it done on your car with no damage.
back in the day, pre Internet, i went to the library, broke out my card and took out chiltons manuals. you guys today got it easy with all the forum help, and you tube vids out there.
like bio said, its just nuts and bolts.