Open Google Calendar
Click the event you want to share
Click Edit event
Under Guests, enter the email addresses of the people you want to add
Click Save
Choose whether to send invitation emails
For a new event, click Create, add the event details, enter guest emails under Guests, then click Save
To share an entire calendar, open Settings
Select the calendar you want to share
Go to Share with specific people
Click Add people
Enter the email addresses
Set their permission level
Click Send or Save