To access your campaign performance data via reporting API, you can create a report with necessary parameters as defined below. Please note, once a report is created, you can re-use the same report to fetch latest data. For instance, if you create a report for duration as "Last 7 days", this will be a rolling window and will always fetch last 7 days data depending on when you query the report.
Try It! to start a request and see the response here!