To greet a friend or another Indian, We join our hands (palms together), bow down in front of the other person, and say Namaste, Namaskar, or Pranam.
The Lord dwells in the heart of every human being. This joining of hands symbolizes the meeting of two souls, our real self actually meets Itself. This signifies reverent Salutations and Unity of Souls.
Bowing down & joining hands symbolizes humility and also makes us humble. Thus when we joins our hands and say Namaskar, we actually see the Lord in the other persons and believe, "I bow with deep respects to the all-loving, all-powerful and omnipresent (present everywhere) Lord in you."
