Nick reports directly about his first experience of Gatsby's parties in chapter 3. From the beginning he notices that people arrive early in the day to swim and play during the afternoon while great canvas tents are pitched, orchestras set up, and lemons and oranges arrive to be freshly squeezed for drinks.
Something worth great note is the typical party attendee. Nick specifically points out twice that he is one of few people actually invited to the party. Many people just show up with no relationship to the host. They leave the same way. Nick noticing free dancing, singing, and play throughout the evening. As people meet each other he comments that tones seem casual and he suggests that what occurs here is surface level and forgotten later.