1) Make sure that you downloaded the iCal file.
2) Open Google Calendar
3) In the top right, click the Settings menu button -> then click the Settings
4) Scroll down the menu on the left side and click the Import-Export button
5) Click Select file from your computer and select the file you exported. The file should end in ".ics" or ".csv."
6) Choose which calendar to add the imported events to (by default, events are imported into your primary calendar)
7) Click Import