Hands are often used in greetings. The most common form of greeting is shaking hands, of which there are many different forms. Opening the palm shows that there is no concealed weapon. This is significant in greeting, salutes, waves etc.
This is one of the few times we are allowed to touch the other person and it may get used to send various signals.
Dominance is shown with hand on top, strength, prolonged holding ('I decide when to let go') and holding the person with the other hand.
Affection is shown with speed and duration of shake, touching with the other hand and enthusiastic smiles. The similarity between dominant and affection handshakes leads to tricky situations where a dominant person pretends to be friendly.
Submission is shown with a floppy hand, palm up and which is sometimes clammy and with a quick withdrawal."