Use case:
User should be able to create a recurring event, say every Monday and Wednesday for a month.
Solution:
1) Navigate to My Calendars > Calendar Controls > edit calendar.
2) Edit your desired calendar and in the edit screen go to “Fields to display on create and edit dialog”
3) Here ensure “Create Recurring Series of Events” is in the selected list of fields
4) After saving in the previous step, you are now ready to make recurring events.
5) To create a recurring event, click on the appropriate spot on the calendar and select the desired calendar (for which you have executed previous steps). In the create screen, you will now see a dropdown which allows you to specify recurrence. In this case, we want an event to repeat for a month every Monday and Wednesday. Select the “Every N week(s) on days” option.
6) This option will enable several relevant fields (Days of the week selection, recurrence start and end dates) that will help you setup the recurring event. Hit save after the appropriate selections.
7) Your recurring events should now be created.

NOTE: recurring events can only be set up against the Event(Activity) Object