How do Salesforce reports works?

We have several custom objects that store Mailchimp data in Salesforce. These objects can be used in Salesforce reporting. In our package, we provide some sample reports, which can be found:

• Within the app, in various locations, by clicking the reports button. For example, on the Audience Summary page, you can access reports about members, imports, campaign activity, and more, all filtered to that one audience.
• On the Campaigns list in an Audience, via the pull-down action menu, for a campaign activity filtered to that campaign (https://jmp.sh/3xQEAYWP) 
• In the Mailchimp reports folder, which can be accessed using the standard Salesforce reports tab.

Also in the package are several Salesforce report types you can use to build your own Salesforce reports.

• Mailchimp Accounts - Connected account(s). It is the parent to many of the objects below.
• Mailchimp Audience - Audience/list in Mailchimp. It includes aggregate stats and defaults.
• Mailchimp Campaigns - Email campaigns sent. It includes stats for the mailing.
• Mailchimp Email Activities - Optional (more info). Every engagement a member has with a single email.
• Mailchimp Group Categories - Group classification. (more info)
• Mailchimp Groups - Grouping of Mailchimp members
• Mailchimp Imports - Data Wizards. Includes data on data wizards like status and schedule
• Mailchimp List Histories - On-going monthly stats for each audience
• Mailchimp Members - Audience members and their current status. An email will only exist once per list.

Related: How do I show campaign fields on email activity reports?