By default, everyone has limited access to your calendar. As they create a meeting invitation using the Scheduling Assistant, they will be able to see whether you are free or busy, but they won't be able to see any other information about your schedule (such as the meeting title, who is invited, or where it's taking place).
Sharing your calendar allows people to look at the items on your calendar in more detail, but this is still "read only" access. They can't add or change items.
If you want to allow someone to add or change items, you need to use Delegate Access, not sharing.
To share your calendar:
- In the Navigation Pane, click Calendar.
- In the toolbar, click on "Share Calendar".
- An email message will open with the subject "Sharing invitation." Fill in the "To" field with the person you want to grant access to your calendar.