In recent days, select tournament referrees declared that creating a pool rack by "tapping", rather than placing then setting with the traditional wooden rack most use instead, is the superior rack building method. I want you to learn how to tap, but also how to tap balls into place without harming the pool table itself.
The referees used lined markers atop the table felt to best set each ball in place by hand. Most tables you shoot on do not offer such a luxury accessory as these clean outlines that resemble chalk lines (lines which can distract you visually during play, anyhow). Use the wood rack and tapping together, instead, and make a superb, legal rack to thwart the other player.
Tightly racking object balls together ensures better defense in the game. Most players aren't competent enough to sink balls consistently on the break, but a loose rack yields an easy scattering of balls, especially those balls at the three corners of an 8-Ball rack or the four end corners of the 9-Ball billiards rack.
To tap a ball into its final resting place, take an extra ball and lightly rap atop its middle, pressing the base of the ball where it touches the cloth down with a straight-line vertical motion from ball top to bottom. The tap need not be perfectly up and down in motion, your other hand will steady the tapped ball and keep the momentum dispersed down into the table in place with ease.
A gentle tap or two on the head ball of the rack, and perhaps the two balls behind it also, is all that is needed on most tables to ensure an extra-firm ball racking. Only referees in pro tournaments need rap all 15 or 9 balls.
Hard raps in the rack, or those made by throwing the balls onto the table at the start of play, are the bane of every billiards room owner in the world. Hard raps create micro dents on the table slate underlying the cloth. These microscopic spots accrue and become "wobble spots" over time that no cloth replacement can repair. Balls traveling slowly over these spots will go far offline, ruining a shot.
Tap gently and watch your opponent try to get a good scatter with a lazy break on your new, tight pool rack. It won't happen!