• Open Google Calendar.
• In the top right, click the Gear icon and then Settings.
• Click Import & Export.
• Click Select file from your computer and select the file you exported. The file should end in "ics".
• Choose which calendar to add the imported events to. By default, events will be imported into your primary calendar.
• Click Import.

The quick method:

• Click the Download button above
• The downloaded .ics file should appear in the application dock at the bottom of the screen
• Click on the downloaded .ics file to sync with your calendar

If the above method doesn't work for you, please try this instead:

• Open iCal
• Select File | Import | Import... from the menu
• Find and highlight the desired .ics file
• Click Import
• Select the iCal calendar to which you want the imported events added
• Select New Calendar to create a new iCal calendar for the imported schedule
• Click OK