No one has ever been formally invited to Gatsby's party but Nick. They also never meet Gatsby. After wandering around the mansion Nick runs into a man, not knowing it's Gatsby.
Nick and Gatsby talk about how they both served in WWI. Gatsby then says to Nick "You look familiar" the irony of that is Gatsby knows its Nick Daisy's cousin.
After Gatsby gets called away for a important phone call. Jordan then had a chat with Gatsby, she comes back to Nick and taunts him with the "tantalizing" news, but doesn't reveal a thing.
Gatsby picked up Nick at his home, for lunch. Gatsby begins to explain his past; Hes the son of wealthy midwesters, he was educated at Oxford, he says he's from San Francisco. Gatsby is so extra with showing proof that he is who he says he is. Once in the city Nick meets Mr.Wolfsheim when meeting him he also sees Tom Gatsby has disappeared by now.
After Gatsby disappears Jordan explains to Nick of how Gatsby and Daisy met in Oct. 1917. Everyone believes that after Daisy's honeymoon she was in love with Tom. But Daisy still loved Gatsby.