ok.. i think you should go read the beginners thread or one of the articles around here for that, basicly you snap ur wrist with you make contact with the bird
i suppose what he meant was how to use the wrist to hit a bird with more power and more effectively. first of all. do u know how to grip your racket correctly. but even if u do. we hardly use our wrist alone. we will normally generate power with our arms, wrist and fingers altogether. with appropriate allocation of power generated by those parts to deal with different situations. let's say if u were asking about "wrist only" shot. then no doubt, my answer is "gripping a racket properly."