That's pretty much the gist of it, although there are some other rules too. But yes, nonprofits can charge money for services and/or pay their staff. Think about Goodwill, probably one of the better known not-for-profits out there. They charge for their clothes, and they pay their employees, but they don't make anyone any "profit" because they funnel the revenue back into their programs, like Skye said. But tax laws, to my knowledge, never prohibit you from paying a reasonable compensation for legit services from employees/directors.