First, make sure you’re signed in with your Yahoo! ID.

Click the Add Event link at the top of the Day, Week, or Month view of the group calendar. Or, if you’re viewing by day, click any hour to add an item to the calendar. Enter the time, date, and description of your event and click Save.

If you wish, you can also set an event to repeat, and set up email notification reminders. You can schedule events for any time. To view event details, just locate the event and click its title.

Note: You may not have access to your group’s calendar. Each group's owner can restrict access to certain features, including the group calendar. If you don't see the link described in the instructions, then you don’t have access. You can contact the group's owner by sending an email to: groupname-owner@yahoogroups.com where "groupname" is the exact name of the group.