To add a new appointment, select Create Appointment from the top-right corner of the Calendar. This will open the Create Appointment window, where you can enter the following details for the appointment:

A button is also available in this window to swap the records listed for Attendees and Regarding in case of mistaken entry. 

Once you have entered the necessary details, the following options are available:

Creating a New Appointment from a Record Summary

It is also possible to add an event attended by a specific record by selecting the appointment icon underneath their display picture in the record summary.

If you have any Appointment Templates set up, you will be prompted to choose one to base the appointment on if necessary. Once you have chosen a template, select Next to continue to the new appointment window explained above.