You can create an audience either in Salesforce or Mailchimp. If you create the audience in Salesforce, it will update Mailchimp almost instantly.
If you create an audience in Mailchimp, it will appear in Salesforce when the sync next runs, typically every hour. You can also manually run the sync via the settings screen.
Below is an interactive demo covering the steps to create an audience in Salesforce.
https://app.arcade.software/P3oHZsSj6K3R8JpNHoUV?embed
