Point Scoring
In tennis, points within a game are counted as 0 (called love), 15, 30, 40, and game. When a player wins their first point, the score becomes 15-0 or 0-15 depending on who won. The scoring continues to 30, then 40. Once a player reaches 40, they need one more point to win the game, unless the opponent also has 40 points.
Deuce and Advantage
When both players reach 40 points, the score is called deuce. From deuce, a player must win 2 consecutive points to win the game. If a player wins the next point after deuce, the score becomes advantage for that player. If the player with advantage wins the next point, they win the game. If they lose it, the score goes back to deuce.
Games and Sets
A set is won by the first player to win 6 games, but they must win by at least 2 games. So a set could be won 6-4, 6-3, or 6-2. If the games reach 6-6, a tiebreaker is usually played in professional tennis. A tiebreaker is a special game played to 7 points (win by 2), and winning it gives a player the set 7-6.
Match Format
A professional tennis match is won by winning the required number of sets. In men's matches, this is usually best of 5 sets (first to win 3 sets). In women's matches and most men's matches, it is best of 3 sets (first to win 2 sets). Some tournaments have different rules, but this is the standard format.
Tiebreaker Rules
In a tiebreaker, points are counted as 1, 2, 3, and so on instead of 15, 30, 40. The first player to reach 7 points wins the tiebreaker if they lead by 2 points. If the score reaches 6-6 in a tiebreaker, play continues until one player leads by 2 points. The player who wins the tiebreaker wins that set 7-6. 
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