The administrator can set the vacation quota for each employee by going to his profile.
Go to the 'Employees' tab, choose an employee and add their vacation quota like this:
Don't forget to save your changes after entering values.
The vacation counter will then keep track of the number of remaining vacation days for each employee.
You can check how many vacation days employees have left on any given day. Just choose a day on the employee's timeline and click on it. You will find the vacation quota information on the right side of the screen.