To book a vacation go to the Settings tab on the left hand side menu.
Under the Your Settings title select Hours/Vacation.
This will now show your settings options on the right hand side. Click on the "Vacations" section and a new pop up window should appear.
In this pop up window you will want to select "+add a vacation" button at the top right corner of the window.
This will pop up a new window where you can fill in the start and end date of your vacation.
Hit save and you're all set. Your vacation will now be booked off for you in the calendar.