In baseball the World Series is the championship games of Major League Baseball in North America, played in October after the end of the regular season between the pennant winners of the American and National Leagues. The Series winner is determined through a best-of-seven playoff, meaning that the first team to win four games wins the series. The World Series has been an annual event since 1903. It is played at the baseball stadiums of the two teams in the series. Baseball is so popular that it is sometimes called the “national pastime.” The word “ballgame” in the United States almost always refers to a game of baseball, and “ballpark” to a baseball field.
The rules of baseball can be found here http://aupairinamerica.com/resources/life_in_the_us/baseball.asp