On the next screen, edit the name, etc. and choose the auto-refresh frequency (from every 5 min. to every week). Click OK.
See also instructions from Apple. If you’d like to have iCloud to push a Calendar feed to all your Apple devices, subscribe it on your Mac (not on iPhone or iPad), make sure to choose “iCloud” as the Location as described here.
iPad / iPhone
For iPhone users, in most cases tapping the iCalendar feed URL will launch the calendar application and the feed subscription dialog appears. If that is not the case for you, follow these steps:
On the Home screen, tap Settings.
Tap Calendars (just below Mail, Contacts)
Tap Add Account
Choose Add Subscribed Calendar.
Tap Next. If you want to enable reminders, turn on the Events Alerts (make the button green so that you can set up reminders) and done.