There are two ways to add breaks to shifts.
1) When creating a shift, you will see this popup.
To add a break, check the 'This shift includes a break' checkbox. You will then see two options.
i) If the shift always has the same duration of break (say 30 minutes), then type 30 into the 'Break Time (mins)' text box.
ii) If the break duration depends on the staff member, check the 'Defer to employee default' checkbox. In this case, you will need to set the length of break for each employee.
You can do this by going to the employees area of the site,
And selecting to edit the employee by the orange 'Edit' button next to their name,
On the 'Additional Information' tab you will see a field for 'Break Time (mins)'. Here, enter the duration of break that this staff member is entitled to.
This will deduct a break of the specified duration from each shift (scheduled to include a break) the employee is scheduled to work.