Here is a guide for the beginning pool player starting with the most popular game in pool:
8 Ball- (Large Triangle)Balls are racked randomly except the 8 ball must be placed in the middle which is the third row from the top of the rack along with 1 solid (numbers 1-7) and 1 striped (numbers 11-15) ball on each of the back corners of the rack. Contrary to what many believe, the 1 ball does not have to be placed at the top of the rack. That is only on rotation games where the lowest numbered ball on the table must be struck first to be a legal shot. The ball in the top position should be seated on top of the spot with all balls behind touching.
9 Ball-(Diamond)Balls are racked with the 1 ball sitting in the top position, the 9 ball in the middle with the remaining balls racked randomly. It is common for the 2 ball to be placed in one of the three positions behind the 9 ball although this is not an official rule. The 1 ball at the top of the rack should be seated on top of the spot.
10 Ball-(Small Triangle)Balls are racked with the 1 ball sitting in the top position, the 10 ball in the middle with all other balls placed at random.
This is an overview of how to rack for 3 different games of pool that are popular today. Always clarify racking rules with your opponent and/or tournament director as there can be variations such as in an 8 ball rack requiring the 1 ball at the top of the rack with alternating solids and stripes on the outside of the rows behind it. In the U.S. Open 9 ball tournament, the 9 ball is seated over the spot instead of the 1 ball. The intention is to make it more difficult to make a ball on the break but from what I see, most of the pros have it figured out. The guidelines I’ve put forward here are common to all of the leagues and tournaments that I know of but remember, house rules supersede all others. When in Rome, do as the Romans do!