Yes, the designated hitter is only used in the American League. Pitchers typically bat 9th in the National League.
In baseball, the designated hitter rule is the common name for Major League Baseball Rule 6.10, adopted by the American League in 1973. The rule allows teams to have one player, known as the designated hitter (abbreviated DH), to bat in place of the pitcher. Since 1973, most collegiate, amateur, and professional leagues have adopted the rule or some variant. MLB's National League and Nippon Professional Baseball's Central League are the most prominent professional leagues that do not use a designated hitter.
In baseball, a pinch hitter is a substitute batter. Batters can be substituted at any time while the ball is dead (not in active play); the manager may use any player who has not yet entered the game as a substitute. Unlike basketball, American football, or ice hockey, baseball does not have a "free substitution rule" and thus the replaced player in baseball is never allowed back into that game. The pinch hitter assumes the spot in the batting order of the player he replaces.
The player chosen to be a pinch hitter is often a backup infielder or outfielder. In the major leagues, catchers are less likely to be called upon because most teams have only two catchers, while pitchers are almost never used as pinch-hitters, because they tend to be worse hitters than other players on the team. The pinch hitter may not re-enter the game after being replaced with another player.
The American League of Professional Baseball Clubs, or simply the American League (AL), is one of two leagues that make up Major League Baseball (MLB) in the United States and Canada. It developed from the Western League, a minor league based in the Great Lakes states, which eventually aspired to major league status. It is often called the Junior Circuit because it claimed Major League status for the 1901 season, 25 years after the formation of the National League (the "Senior Circuit").
At the end of every season, the American League champion plays in the World Series against the National League champion. Through 2013, American League teams have won 63 of the 109 World Series played since 1903, with 27 of those coming from the New York Yankees alone. The 2013 American League champions are the Boston Red Sox. The New York Yankees have won 40 American League titles, the most in the league's history, followed by the Philadelphia/Kansas City/Oakland Athletics (15) and the Boston Red Sox (13).