If you'd like to follow along with the small seasons calendar via iCal, you'll want to create a new calendar subscription. On Mac, you can do this by going to File > New Calendar Subscription…
Into the panel that opens, paste the following URL:
After a few seconds you should see events for every small season, about every two weeks or so. If you run into any difficulties, please create an issue on the Github repo and I'll be happy to help you out.
Enjoy, and I hope it helps you stay in tune with the world around you :)