how to add an internet calendar in your calendar app

MacOS

In Calendar, choose File > New Calendar Subscription

Enter the calendar’s web address, then click Subscribe

Enter a name for the calendar and choose a color to help you identify it on your calendar

Choose iCloud from the Location menu, then click OK

iPhone/iPad

Open the Calendar app

Select Calendars at the bottom of the main view, then select Add Calendar

In the popup, select Add Subscription Calendar

Paste the link to the calendar, then tap the Subscribe button and tap Save

Google

Google Calendar

On your computer, open Google Calendar

On the left, next to Other Calendars, click Add other calendars, and select From URL

Enter the calendar’s web address, then click Add Calendar