How do people who run non-profit organizations make money legally?

I've taken a college course on introduction to business and we did a huge segment on non-profit organizations. We "learned" on how there is a lot of money in non-profit organizations, and people can make strong livings by forming them. I understand how a NPO can raise money for it's own cause via fundrasing, grants, donations, ect.. But, how do the starters and employees of NPO's make their own personal funds legally? It doesn't make since besides tax exemptions.