Calendar is the same register as Schedule, drawn by date. It shows due dates and completions. It does not hold a separate list of audits.
Read the month
Open Auditing, then Calendar. Events come from the schedule. Move through the months to see what is due and what has been completed.
Open or add an audit
Click an event to open that audit and work through its checklist. If you are allowed to create audits, you can add one from the calendar as well. The new record still needs a title and a due date, and it appears on the schedule.
Dates, status, and scope are edited on the schedule. The calendar is the place to see whether the month is crowded before you generate another plan.