What are the freemasons, illuminati or masons in general?

There is so much talk going around in the media and everywhere. What really are the freemasons or the illuminati? Why do people not like them so much? I've tried researching it, but I still don't completely get it. Are they just devil worshipers? I'm really just looking this up just to learn more about it. Any insight would be greaattllyyy appreciated.