Along with booking team members on various projects, you can also schedule their time off. Use this feature to add a vacation, sick leave or any custom time off where a person will not be available for a certain period. You can also use this feature to make a sales reservation for them, which will prevent them from being booked elsewhere.
Go to Settings > Time off categories to see the list of available time off events.
You can edit time off events and set them as paid or unpaid. This will affect your time reports and costs. See this article for more information about paid vs. unpaid time off.