I was wondering,how can I become a Bicycle Mechanic?

I mean,I know in order to do that one need to know about how to deal with Bike Problems,but the question here is: How did Bike Mechanics learn how to do and fix up the Bicycles?

Back in my Fathers day,all he had to do was go to a Bicycle Shop was watch how the "Uncle Bicycle" fix the Bikes but these days if you try and do that,things will go absolutely awkard for some reason.