HR users can define new days off that will not count to used days when creating new Vacation Document. Every new created holiday can be defined as one time only or yearly, or in , or recurring (e.g. New Year's Eve that reoccur every year at the same date). In case of workdays - HR creates schemes of non working days of week week.You can access this panel as HR User , that can be assigned to different users.
Holidays management
While being logged as a member of HR group (Jira HR group picked at initialization), from Navigation Bar Menu ➜ go to Management (1) ➜ Holidays (2). To add a new vacation, please user "Add vacation" button. 
Holiday Schemes (2). To make changes, click on click "Edit" hyperlink (3)
Edition button for a holiday scheme is also visible after clicking on a desired scheme's name. If you do not wish to go with creation of new holiday scheme(s) and assign particular users to it, then fast track mode is enough for you (i.e. working only on Default holiday scheme). In such case, you may use "Add holiday" button (5) on that step directly, to add off-work day to the desired scheme's calendar.
To create a new holiday scheme, please go to "Holiday Schemes" (2) and here you can add a new one. After pressing "Add holiday scheme" button (4). In the appeared prompt just type its name and press add. To populate it with off-work days, follow the below steps.
%20-%20accessing%20vacation%20days%20management.png?version=2&modificationDate=1519047619538&cacheVersion=1&api=v2)
Adding new holiday
When editing a desired holiday scheme, you should see a similar view, like the one below. To add a day that will not be treated as a compulsory working one, please use "Add holiday" button:
%20-%20edition%20of%20holiday%20scheme%20to%20add%20free%20of%20work%20days.png?version=1&modificationDate=1519036327414&cacheVersion=1&api=v2)
Prompt should appear:
%20-%20add%20new%20holiday%20prompt.png?version=1&modificationDate=1519036657526&cacheVersion=1&api=v2&height=250)
To add new holiday you can also click on desired day in calendar and then fill up its name, Next, choose holiday type: One time - for selected year only, Yearly - for all years in selected day. Be advised - this can be done whilst being in edition mode of particular holiday scheme.
After filling in all necessary options and deciding if the event should reoccur every year, you can press "Add" button to place it in the calendar of a particular holiday scheme (1):
%20-%20event%20added%20to%20the%20calendar.png?version=2&modificationDate=1519038970655&cacheVersion=1&api=v2)
Removing existing holiday
To remove holiday, simply click its name on calendar and in "Edit holiday" prompt click the "Remove" button.
Workdays
Access to Workdays schemes, its creation and edition is quite similar:
%20-%20workweek%20schemes.png?version=1&modificationDate=1519047182682&cacheVersion=1&api=v2)
Whilst being logged as a Jira's HR group user, from Navigation Bar Menu go to Management (1) ➜ Workweek Schemes (2). Now you can access workdays scheme's name to view it, or click "Edit" hyperlink directly. Currently viewed/edited workweek scheme is displayed below "Workweek schemes" (3). Whilst being in read only mode, you can quickly switch to edition by pressing "Edit scheme" (4) button.
You can choose what days of week will be marked as workdays. Every unticked day will be treated as a bank holiday and thus not taken out from user's total (e.g. yearly annual leave) quota.
After any changes made, you need to click Update workdays button to apply them in your system. By default, any day of week (except Saturday and Sunday) is set as a working day.
...
Next Vacation Manager HR Management - Managing Vacation Definitions