1. Go to http://www.apple.com/icloud/setup/mac.html and establish your iCloud account, if you have not done so already (requires OS 10.7.2 or later).
2. Open iCal on your computer.
3. Go under the iCal menu at the top right, and select Preferences...
4. Under the Accounts tab, click the "+" button.
5. On the resulting screen, select iCloud from the Account Type: drop down menu.
6. Enter your Apple ID and Password.
7. Click Create.