Open Google Calendar
In the left panel, find the calendar you want to share
Hover over the calendar name
Click the three-dot menu next to the calendar
Select Settings and sharing
Under Share with specific people or groups, click Add people and groups
Enter the email address of the person you want to share with
Choose the permission level
Click Send
To make the calendar public, go to Access permissions for events
Check Make available to public if needed
Choose the visibility or permission settings
Save your changes