What is the illuminati?

I heard that celebs and music ppl lke Jay Z, Beyonce, Taylor Swift, Kanye West are apart of it. Do they worship/sell their souls to the devil? They do that pyramid sign with the hands and stuff it scares me. I couldn't bring myself to believe that Beyonce and Taylor Swift would do this stuff. Also, i heard some celebs died because they didn't want to be apart of the illuminati. Sad. Help me out and explain this stuff please???????????????????????