What category is mostly watched on youtube, how does some ppl make money there?

just would like to know, how do ppl get really good videos on youtube, is there a certain type of thing or topic ppl like to watch ppl, have shows on there, some ppl create video of cartoons on there at what point can you actually make a career when you upload your own videos, i know of some guys who record their skateboarding stunts and get over s million view, just would like how to make your videos popular on youtube