Pick the calendar you use. Each one opens a “subscribe” screen; say yes and you’re done. New activities appear as leaders approve them, without you doing anything.
iPhone, iPad or MacOpens the Calendar app’s Subscribe screen. Tap Subscribe, then Add.
Google CalendarAsks “Add calendar?” — say yes. Works from a computer or the web; it then syncs to the phone app on its own.
Outlook — work or school accountOpens Outlook’s “Subscribe from web” with the address filled in (sign in first — if it only shows Outlook’s home page, use Add calendar → Subscribe from web with the address below).
Outlook.com — personal accountSame thing for a personal @outlook.com / @hotmail.com calendar.
Anything else
Most calendar apps have “subscribe to a calendar” or “add by URL”. Give it this address:
It refreshes on its own: Apple checks about once an hour (Settings → Calendar → Accounts → Subscribed Calendars to change it), Google roughly once a day. Just want one activity? Every post on the home page and in the weekly email has its own Add to calendar links.