The guide below refers the Apple Calendar app. The flow is similar for other calendar apps.
Go to the Shiftkeeper home tab.
In the schedule list, click on the ... button and then Export.
Copy the displayed iCal URL.
Open the Apple Calendar app.
Choose File > New Calendar Subscription.
Enter the copied iCal URL, then click Subscribe.
Adjust the subscription settings as preferred and click OK.
Any changes to the schedule shifts will be reflected in the calendar feed automatically, no manual updates are needed.
Changes might take some time to be reflected in your calendar, depending on the auto-refresh period you have selected for the calendar subscription.
Shifts which have finished more than two months ago are not exposed in the calendar feed.
To remove a schedule from your calendar app, simply delete the calendar subscription.
For example, in the Apple Calendar app, you can do this by right-clicking on the calendar from the list, and then choosing Unsubscribe.