The Repeat Occurrance feature allows you to schedule an event that repeats over and over again on a regular basis.
For example, the standard every-other-weekend visitation (EOW) schedule is a repeating event. Other examples could be a meeting that occurs on the first Tuesday of every month or a club that gets together every 6 weeks.
Your OPTIMAL Calendar can schedule all of these kinds of events and more, including 1st, 3rd, and 5th weekends. Just tell the calendar what the schedule is, and it does the rest.
For some examples of setting typical repeating schedules, click here.