Racking and Shooting the Balls
At the beginning of every eight-ball game, all of the balls except for the solid white cue ball must be racked by placing them in the triangle at the lower end of the pool table. Place the black 8 ball in the center of the triangle, and a solid and striped ball on opposite corners of the triangle. Once the balls are racked, remove the triangle and place the cue ball on the line on the opposite end of the table.
With your cue stick, "break", or shoot, the cue ball into the group of racked balls at the other end of the table. If no ball is pocketed after the first break, your opponent is allowed to shoot the cue ball next. Continue alternating breaks until a player pockets a ball. Once a player pockets a ball, he is given either solids or stripes depending on the ball he shot, and the opponent is given the remaining group of balls.
Gameplay Rules
Throughout the game, if the 8 ball is pocketed before all of the player's other balls have been pocketed, the player automatically loses the game. To avoid illegally pocketing the 8 ball, refrain from using dangerous trick shots when one of your balls is close to it. If avoiding trick shots like shooting the ball off the side of the table isn't possible, angle your pool stick to reduce the chance of knocking the 8 ball into the nearby pocket. Angling the pool stick higher, lower, to the left or to the right is also very helpful when your ball is too close to your opponent's ball or sandwiched between other balls.
Scratching occurs when the white cue ball is illegally pocketed during a shot. If a player scratches, the opponent is allowed to physically move the cue ball. In some eight-ball pool games, the player can move the cue ball anywhere on the table, while in other games the player can only place it on the shooting line on the opposite end of the table. Make sure to clearly establish scratching rules before starting the game for a clear understanding of what you are allowed to do when either you or the other player scratches. Scratching can occur at any time during the game, and can make the difference between a win and a loss for a player. Scratching is usually the result of the cue ball being hit too hard or too close to a pocket.
Players can continue to pocket their group of balls until they miss a shot, at which point it becomes the opponent's turn. When a player has pocketed all of her balls, she can legally pocket the 8 ball to win the game. However, if a scratch occurs on the final shot and the cue ball is pocketed along with the 8 ball, the player automatically loses the game. For more in-depth rules for eight-ball pool, follow the link in References.