The poor creature is first removed from the tank and dumped into the sink. When the chef is ready, he would grabbed the lobster and twisted it into half from the middle (refer to pic) while it's still ALIVE! And the meat from the tail portion would be served after the shell is removed.
What about the head, you may wonder? Don't worry, nothing is wasted.
It will be used as a deco of course! Just beware, its feelers and legs might still be MOVING when it's served in front of you!