The National League (or NL) is one of the two leagues that make up Major League Baseball (MLB). As of the next MLB season in 2013, the NL will have 15 teams. At the end of each season, five of these teams go to the "post-season" where one will win the National League championship. The champions of the National League plays against the champions of the American League in the World Series. The team that wins the World Series is the champion of Major League Baseball.
The only big difference between the National League and the American League (AL) is that the AL uses the "Designated Hitter" (or DH). The Designated Hitter is a player who does not play in the field, but is used to bat for the worst hitter in his team's "lineup", usually the pitcher. The NL does not use the Designated Hitter, and all players in the side must bat and field for themselves.