iCal and Google Calendar Syncing
To do so just:


On iCal go to Preferences / Accounts.
In the panel on the left, click the + button to add an account.
Fill in the information, being:


Account Type: Google. Although you can either use Automatic or CalDAV, and the System will detect the proper account type.

Email Address: The email which you are using to log into the Calendar. The @domain.com part should be written too.

Password: Well, the password for that account. If you are using 2-Step verification you must use an application-specific password.

Doing this, by default, will sync any calendars that appear in My Calendars on the web, as well as the Contact's birthdays and events.

Adding additional calendars, or removing any of them from syncing, you must go to the Account Sync Configuration Page, and select the calendars you'd like to be displayed. After doing so, refreshing iCal will display the new configuration.