Open the calendar that you wish to subscribe to
Click the Add + on the bottom right
On the left, next to “Other calendars,” click Add + > Subscribe to calendar. If the calendar has been shared with you, you’ll get an email.
In the “Add calendar” box, enter the person's email address, or select one from the list.
Press Enter.
Depending on whether their calendar is shared, one of the following happens:
If the calendar isn't shared with you, you'll be prompted to request access.
If the calendar is already shared with you, their calendar will be added on the left side under "Other calendars."