Open Google Calendar
In the left panel, find My calendars
Hover over the calendar you want to share
Click the three dots next to the calendar name
Select Settings and sharing
Under Share with specific people, click Add people and groups
Enter the email address of the person or group
Choose the permission level
Click Send
To share publicly, go to Access permissions
Enable Make available to public if needed
Choose the public permission level
To share with your organization, enable Make available for your organization if available
To stop sharing, remove the person or group from the sharing list
To change access, edit the existing permission level