As an admin or manager, you can book holiday on behalf of the staff you manage. (Admins can do this for all users, while managers can only book holidays for their direct reports or any users who they are set as a holiday approver for).
If you wish to book the same date/s for more than one employee, you can do so in one bulk action. To do this:
Open your Staff Squared calendar.
Click 'Add New'.
Remove 'You' from the booking form.
Click 'Select more staff'.
Select the staff members you wish to add the date/s for, or, select 'everyone' if you need to add the date/s for all employees (note that this will include yourself).