As a calendar owner or a user with Edit permissions, you can manipulate with events from other sources within your calendar. Navigate to Calendar Settings → Integrations:
Export Calendar to iCal formart
This functionality allows you to get a snapshot of your calendar events in iCal format. This snapshot can be imported to another calendar, for instance, to Google Calendar.
To export the current calendar push the "Export" button. Calendar's issues and events will be downloaded to your computer as an iCal (.ics) file. Following is the example of Calendar events imported to Google Calendar from .ics file:
Import from iCal file
This functionality allows you to upload a snapshot of events exported from another calendar (i. e. Google) to your calendar. Read: Export your Google calendar.
Select the exported file and import it to the calendar. Imported events are added as Non-JIRA Events with default color. Following is the example of the event imported to Calendar:
Google Calendar Sync
This functionality allows you to fetch a single google calendar (public or owned by you) to a particular calendar. Any user with access to the calendar in Jira will see the events that you fetched to this calendar from Google.
The functionality only works if global integration settings are all set, so in case of any troubles contact your Jira Admin.
Firstly, you will need your Google Calendar ID. Follow the steps to find it:
Open your Google Calendar app page using your Google account.
Navigate to your subscribed/available Google calendars list (usually bottom left side).
To get to your calendar settings, hover over the calendar you wish to work on and click the three vertical dots that appear to the right – this will bring up a dropdown menu, click Settings and sharing.
Press the Import button, then in case of a private calendar, you will need to authorize your Google account.
Google Sync Troubleshooting
If the Authorize button doesn't appear, open the Developer Tools, navigate to Console and check if there are any errors (marked red). Possible errors:
Cookies are not enabled
Ensure that you are not in the incognito mode in your browser since you will need to authorize to access the Google Calendar data.
API Key not found
API Key in the global Calendar settings doesn't match the target google project API key. Check if the API key exists in the google project (the Credentials section) and that it is specified in the global Calendar settings.
Not a valid origin for the client
In case the correct URI is set for the Client ID and the error still exists, generate a new Client ID with the required URI.
Other google API errors and handling methods can be found here: https://developers.google.com/calendar/api/guides/errors