If you win your first point, your score is 15. Win a second point and your score
is 30. Third point  40. If you win a fourth point, the game is yours, unless
you and your opponent have won three points  in this case, the score is known
as deuce and you must win by two clear points. If you win the point at deuce,
the score is called advantage to you and you must win the next point to win the
game, otherwise the score reverts to deuce.
The historical origins of the 15, 30, 40 and so on are believed to be derived
from the presence of a clock face at the end of the court. A quarter move of the
appropriate hand was made after each point, with the score being called as 15,
30, or 45 as the case might be. When the hand moved to 60, making the complete
circuit, that was game.
Winning six games wins a
set; except that you must win by a margin of two games. Players change ends when
the total number of games is an odd number (e.g. 10, 21, 32). The tiebreak
system of scoring is often adopted to decide a set which reaches six games all.
A match can be best of 3 sets (you need to win 2 sets to win the match) or best
of 5 sets (you need to win 3 sets to win the match).
In a tiebreak, the player who first wins seven points wins the game and the
set, provided there is a margin of at least two points. If the score reaches six
points all, the tiebreak continues until the two point margin is achieved.
Numerical scoring is used (e.g. 10, 20, 21, 31, etc).
The player whose turn it is to serve serves the first point (from the right side
of the court). The other player serves the second point (from the left) and the
third point (from the right). Each player then serves alternately for two
consecutive points (first from the left and then from the right). Players change
ends after every six points (and at the conclusion of the tiebreak). The first
game of the next set is served by the player who did not start the tiebreak.
