Your reservations from OTA's such as Booking.com and from your own website automatically appear in your diary, however if you receive a reservation over the phone the following should help you add the reservation.
Click on "Add Reservation" in the menu. You can now perform the following
Enter the guest details, or search for a guest who has stayed with you before.
Select the dates, room and rate the guest has requested
Add details of any payments taken e.g. deposits or advanced payments
Add any notes or requirements the guest has
You can save the reservation and optionally send a confirmation as an email to the guest.