To export current calendar click on "Export" button. Calendar's issues and events will be downloaded to your computer as an iCal (.ics) file.
To import events from Google calendar first you need to export the required calendar. Please follow the steps: Export your Google calendar. Imported events are added as Non-JIRA Events with default color.
Before you start set-up integration your Jira admin should configure connection to Teamlead google app.
After pressing the import button you need to authorize in the google calendar.