Appointments are reminders on the Daily which are assigned to a contact (doctor or others). You can optionally receive reminders and save notes about them.

Add (two possibilities):

Network → Select doctor/contact → Appointments → Add appointment
Only on iOS) Daily → “Plus” symbol (top right) → Appointment → Select doctor/contact

Edit (two possibilities):

Network → Select doctor/contact → Appointments → Tap on the appointment
Daily → Tap on the appointment

Delete:

(Only on iOS) Network → Select doctor/contact → Appointments → Swipe appointment to the left
(Only on Android) Network → Select doctor/contact → Appointments → Press and hold the appointment → “Bin” symbol (top right)