While creating or editing an event, open the repeat control and choose the recurrence pattern: daily, weekly, monthly, yearly, or a custom interval. Set an end date or occurrence count when the series should stop.
When you change or delete one occurrence, Calendar asks whether the action applies to that occurrence or to the series. Read that choice carefully. Editing the series can replace exceptions that were made to individual dates.
For an irregular schedule, create separate events instead of a recurrence rule. This makes later changes clearer and avoids exceptions that some connected calendar apps display differently.