His buddy Mercutio had an invitation. That probably helped.
Romeo got invited to the party through a servant who was handing out the invitations on the streets. Romeo happened to come across the servant and the servant mistakenly asked Romeo to read the invitation list, leading to Romeo being invited to the party.
He climbed the wall.
He crashed the party. He wasn't invited.
Benvolio and Romeo went to the Capulets' party with Mercutio and other friends.
he learns that there is a party at the Capulet house. he learns Rosaline is coming and romeo wants to see her
The montagues themselve were not invited. Romeo sneaks himself onto the Capulets guest list when on the the Capulets illiterate sevants asks ROmeo for help reading the list.
A Capulet servant could not read the guest list to the party that his master gave him. So coming upon Romeo and Benvolio, he asks Romeo if he could read. Romeo read the list for the servant and sees Rosalins's name. He asks the servant where they will be and the servant says that '...if you be not of the house of/ Montague, I pray come and crush a cup of wine...' and so they would have been invited to the party if they weren't Montagues. Which of course they were.
He crashed it, with the assistance of his pal Mercutio, who was invited.
They see a copy of the guest list.
No Montagues were invited, including Romeo. Mercutio was invited, but he's not a Montague.
Well, Mercutio was invited. But as for Romeo and the rest, Capulet didn't mind as long as they behaved themselves.
Romeo helps the servant deliver an invitation to the Capulet party by reading the guest list and identifying the people who are invited. This is how Romeo learns about the party and decides to attend, where he meets Juliet for the first time.
Rosaline was on the guestlist. If she hadn't been, Romeo wouldn't have bothered showing up. Rosaline was invited because she is a Capulet, Juliet's cousin.
She got invited to Capulet's party, which made Romeo want to crash it.