This assumes you already have the calendar created in the calendar system.

1. On your teacher web site, create a new page
   
2. On the new page, click the Insert menu and select Calendars. Select the calendar you want to insert.
   
3. On the resulting screen, adjust settings as needed, or just leave them alone. Press Save.
4. Any changes you make to this calendar in your calendar system will now automatically appear on this page.

Note that you'll need to decide if it makes more sense to create multiple pages, one for each class's calendar, or to include all class calendars on the same page. Multiple pages makes the most sense in most cases.