If you're planning a multi-day event and the shift you're adding will repeat on later days, you can set-up repeating shifts. Simply select the repeating pattern you would like from the 'Repeat' dropdown when creating a shift. When you create the shift, multiple shifts will appear in your schedule, one for each instance in your repeating pattern.
Note: the shift repeats, but different people can be assigned to it at different times. It is not an ongoing shift, where one person has the same shift every day, week, or month.
You cannot turn a regular shift into a repeating shift - you will have to create a new shift and set it to repeating.
Choose the 'Custom' pattern to create more complicated patterns, such as 'every Monday-Friday'.