You set the default Leave Settings of an employer by clicking the employer name in the main menu and choosing "Edit Details".
You then choose the "Leave" item in the sub menu.
All of these settings can be overridden on a per employee basis on the employees leave settings
This is the number of days the employee will be given as their allowance for the year
This is the date the allowance will be reset. Only the date and month part are relevant as the year will always be automatically incremented to ensure it's in the future.
If this is ticked then the remaining balance of holiday days will be shown in the employees payslip.
If you tick this option then the above options are hidden as they are no longer relevant. Additional fields are shown instead, these are explained in more detail on the employees leave settings help page.