if you know tools & mm / inch difference, if you can read feeler gauge, if you can test a battery fluid Specfic gravity, test a car generator ( alternator ) with a meter, then you may qualify to learn basics.
start by buying a compression tester, and check compression values WET & DRY for every car in family & friends.
write down make model year & odometer reading when doing compression test.
thats' the 1st step towards learning.