By default, your calendar is shared with everyone in your domain, and they can only see when you're free or busy, not all the event details. However, you can allow them to also see event details or turn off calendar sharing completely.
You can also share your calendar with specific people and give them one of the following levels of access:
- See free/busy information only
- See all event details
- Make changes to your calendar
- Make changes and share your calendar with others