Subscribing adds the organizer's calendar to your personal Outlook.com calendar (outlook.com, hotmail.com or live.com accounts). New and changed events then appear automatically. These steps are for a desktop browser.
Do you use Outlook with a work or school account? Follow the Office 365 article instead.
Before you start
Sign in to Outlook.com in the same browser. The calendar is added to the Microsoft account that is signed in.
Steps
Open the calendar page you received from the organizer and click Add to Calendar. If the page asks for your name and email first, fill them in and continue.
Choose Outlook (online). Outlook opens in a new tab on Add calendar > Subscribe from web, with the link and the calendar name already filled in.
Optionally pick a colour and an icon, and choose where the calendar is listed. Then click Import. Without this step nothing is added.
Outlook confirms that the calendar is imported. Close the window. The calendar is now in the left sidebar under Other calendars.
Good to know
Updates take time. Outlook fetches subscribed calendars on its own schedule. New or changed events can take several hours to appear, sometimes up to 24 hours.
Read-only. You cannot edit events in a subscribed calendar.
Other devices. The calendar belongs to your account, so it also shows in Outlook on your phone once it has synced.
Unsubscribe
Right-click the calendar under Other calendars and choose Remove.
Troubleshooting
Nothing was added. You probably closed the Outlook tab before clicking Import. Go back to the calendar page and choose Outlook (online) again.
Outlook asks me to sign in with a different account. You are signed in with a work or school account. Use the Office 365 option instead.
The Import button is greyed out. The link field is empty. Go back to the calendar page and choose Outlook (online) again so the link is filled in for you.