The screenshot below explains how to easily add a certain appointment:

(Using mouse, highlight the time needed for the appointment and release the button: the new appointment pop-up windows appears. Just enter the text and, if needed, assign Priority, Category, Completion, Alarms and Re-occurrence, then press OK)

Another way:

Press Add button. In the opened dialog:

To enter a non-timed entry for the day: the process is the same, except you need to check the All day event box.

Exclusive appointment - enabling this option for the appointment will ensure that this appointments time will not be taken by any other task. If you will try later to add an appointment with time coinciding with "Exclusive appointment" - EssentialPIM Pro will not let you do it.

All day event - that is the appointment that does not have a certain time, rather, it is assigned to the whole day and will appear on top of each day