How do you spin serve in ping pong?

Answer 1

It is all in the motion of the serve, instead of hitting the ball straight forward, slice the ball with the paddle in order to keep the ball along the entire surface area of the paddle in a more or less downward motion and that will induce spin.

Answer 2

toss the ball in the air, swing your paddle and hit the ball on your side of the table, it must bounce over the net and hit the other side of the table to be a valid serve.