3 Answers

Bob/PKB is on the button... but listen to the Egg.  Some people really do like flirting.  It is a game and it can hurt you if you are not smart.

ATTRACTION:  Generally physical at first.  May be eyes, smile, hair, arms, height, clothes.... there is just something that draws you together.  Voice! Mannerism.
FLIRTING:  Light-hearted banter, sometimes suggestive, sometimes teasing.  catching each other's eye; has to include some touching of hands, knees, shoulders, pat on back
LOVE:  is a many splendored thing.  It's the April rose that only grows in the early spring... Love is nature's way of giving a reason to be living...the golden crown that makes a man a king. 

First people are attracted to each other, one of them may flirt with the person concerned and then they fall in love and usually get married. But some people may just be flirters, they enjoy  it, but when the other person makes a move, the flirter moves on.