Whirlpooling is the process of separating the trub from the wort by utilizing centrifugal force to confine the trub to the center of the kettle so the wort can be drawn off without disturbing the trub cone. Whirlpooling can be achieved by quickly moving the wort in a clockwise or counterclockwise motion until a vortex begins to form in the center of the kettle. Once the vortex has formed, the trub will begin collecting and settling into the center of the kettle, forming a cone as the spinning wort forces the denser particulates towards the center. It is important to allow 15 to 20 minutes for the cone to form before drawing the wort from the kettle. If you are using an immersion chiller, you would want to chill the wort prior to whirlpooling and then draw the wort out slowly as not to disturb to trub cone.
Photo of a 20 gallon boil kettle after the boil had completed and the wort had been whirlpooled and much of the wort had been drawn off.