Once you have selected the employee their profile will appear. Click on Availability.
Click Add New to enter in a new request and a new window will appear. Enter in the start dates and times, the end date and times, and a brief message. When you are satisfied click Save.
The new request will appear on the list.
To learn how to approve/deny request you can read the Managing Time Off Request article.
To read more on managing employees or completing the full profile click here.