Public Post: Everyone can see and shall be used for sharing common information
Public Question: If you need a doctor's advice on something which you feel others could get the benefit, then post a public question. The public question shall be answered by both doctors and other users
Private Question: If you feel you want to consult a doctor privately without sharing the question to others then choose the private questions. This will be only visible to doctors who are in the specialization which you're choosing.