Concerning The Great Gatsby, I'll cover Gatsby for you.
The party is lavish to the extreme. The band is a full band, not a three-piece group that does parties on weekends. Illegal liquor is flowing freely, automobiles abound, people come from everywhere and stay all night. Everyone is reckless. And Gatsby is paying for and responsible for much of it. This is the Jazz Age that Gatsby lives in.
And the same time, he doesn't really take part in any of it. He's not really like the shallow, reckless, hedonistic (pleasure loving) guests at his own party. Notably, he doesn't drink the illegal alcohol, although he does supply it.
The party demonstrates the lengths Gatsby will go just to create an opportunity for a chance meeting with Daisy. He holds the parties hoping that Daisy will happen into one.
She doesn't, so Gatsby takes another step and singles Jordan out and talks with her alone in his house, due to, of course, her connection with Daisy.
Mystery is created about Gatsby because of his alloofness, and his persona and aura are further enhanced at the party.