To access calendar sharing preferences:
1) Click the Preferences link in the top right corner of your account screen
2) Click the Calendar Sharing link under the Calendar section
Free Busy Sharing (Time Blocks Only)
Free-Busy access allows you to share your calendar with reserved time blocks only. All other details of your calendar are restricted.
Read-Only Sharing (Time Blocks plus Details)
Read-only sharing allows you to share your calendar with time blocks and details, without allowing editing.
Full Sharing (Administrative Access)
Full sharing access allows you to not only share your calendar, but give editing and scheduling capabilities to those users you've shared with. *This access level is restricted to members of the system and is not available to non-members.