Go to Your Google Calendar
Go https://www.google.com/calendar, login and and click "Settings" in the top-right corner.
Find the Calendar ID
Click on "Calendars" and then click on the name of your calendar. Scroll down to "Calendar Address" and copy the "Calendar ID" to your notepad. It will have a long string of characters and then @group.calendar.google.com
Make the Calendar Public
Click "Share This Calendar", check the box next to "Make this calendar public" and click "Save".
Download the GCalendar Component
Now that you have your Google Calendar set up correctly, we're going to install the necessary Joomla component. Visit http://g4j.laoneo.net to download the GCalendar component
Extract the GCalendar Folder
Click on the GCalendar folder and extract it so you can see the various extensions inside.
Install GCalendar
Go to Extensions >> Install/Uninstall and click "Browse" to upload com_gcalendar
Go to the GCalendar Component
Go to Components >> GCalendar >> GCalendars
Creating a New Calendar
Click "New" in the top-right corner. You'll see three fields. You only need to give the calendar a title and enter the "Calendar ID" you found and saved earlier. Click "Save"
Make a Menu Link to the Calendar
Go to Menus >> Main Menu >> click "New" >> choose "GCalendar"
Choose the Calendar
Choose the calendar you created and click "Save".