To add an appointment to your email calendar go to Email and select Calendar from the drop-down menu. Alternatively, if you're already in your email, select Calendar from the top menu.
Click on the date you'd like to add the appointment to and a pop-up box will appear for you to complete with details of the appointment.
The 'simple' option only lets you name the appointment and save it to a day, whereas 'detail view' lets you select time, location, importance, set reminders, recurring appointments, notes and invite people from your contacts or email.
Click save to add the appointment to your calendar. If you're running multiple calendars you can also select which calendar to add the appointment to.