I learned that snap shots and portraits are not at all the same. The only similarity they might have is that they both involve people. Not just any picture of someone posing looking good is a portrait. First of all a portrait uses natural lighting from a window of a door slightly open. You capture a moment because the person does not look at the camera as if the person doesnt  know you are there. In simple words it not someone posing  ,more like just being themselves an capturing that . That is what i learned.