If a shift repeats over a period of time it can be entered as a Recurring Shift.
Create a New Shift or Modify an Existing Shift and select the Recurring Schedule option.
The screen expands to show the recurrence options.
Select the recurring frequency - either Daily, Weekly or Monthly.
For Weekly recurrences (as above) enter the repeat period in weeks. For example, if the shift rotates every 3 weeks, enter 3 in the repeat.
Tick which days of the week the shift will repeat on.
For Daily recurrences enter the repeat period in days.
For Monthly recurrences enter the repeat period in months and choose whether the repeat is on the 'day of month' or 'day of week'.
If 'day of month' is chosen then the repeat will fall on the same 'date' each repeat month. For example, if the shift start date is the 2nd July 2014 then the shift will repeat on the 2nd of each month in the repeat period.
If 'day of week' is chosen then the repeat will fall on the same 'day' each repeat month. For example, if the shift start date is 2nd July 2014 then that is the 'first Wednesday' in July. The shift will then repeat on the first Wednesday of each month in the repeat period.
If a recurrence results in a shift falling on a day where no shift is required, such as a bank holiday, then this can be removed from the recurrence by Adding an Exclusion.
If the recurrence should end on a specific date this can be entered by Defining a Recurrence Expiration.
When the recurrence has been entered select 
to save the shift.