Open iCal by clicking the iCal icon in your dock.
Select the calendar you would like to work with from the list of calendars on the left.
Select Export from the File menu.
Select a name from the exported file and then click Export
Log into your Google Calendar: http://www.googe.com/calendar
At the top of the calendar list on the left, click the Add down-arrow button and select Import Calendar.
Click Browse and select the appropriate file, then select Open.
From the drop-down menu, select the calendar to which you'd like to import events.
Click Import to complete the import.