Sign in to your own Yahoo! Calendar account (if you have one). Then go to the public calendar URL that the other person has provided.

Or, you can add the person's public calendar as an overlay to your personal calendar by using the Yahoo! Time Guides feature.

To edit your Time Guides to show a friend's calendar:

1. Make sure that you are signed in to your Yahoo! Calendar account.
2. Click "Calendar Options" on the right of the page, then "Time Guides".
3. Within the "Friends' Calendars" category, click the "Add/Edit Friends" link.
4. Enter the Yahoo! ID of the friend(s) whose calendar(s) you would like to add to your Time Guides, then click the "Add" button. Do not include the "@yahoo.com" when adding friend's names.
5. When you are finished adding Yahoo! ID(s), click the "Done" button.
6. When you return to the My Time Guides edit page, under the "Show on Calendar" column, you can select on which Calendar view(s) you want your friends' calendars to appear by selecting Day, Week, or Month.
7. Click the "Save" button to save your changes.

Note: In either case above, your friend must have activated calendar sharing so you can view their public calendar. If you don't see any events in your friend's public calendar or in your friend's Time Guides, they either haven't activated calendar sharing or the events on their calendar are not marked as "Public." They will need to edit their events so they are no longer marked as "Private."