If you are watching a tennis match and realize that it seems like the points of tennis defy mathematics, you aren't alone. Tennis scoring is quite complicated but hopefully this page will help you grasp the basics.
This is a general guide for scoring. Most of the match is played by following the point scoring system in the left column.
As you hear things like "30 all", "15-40", or "Ad in", you can use this guide to help you follow the score.
If the set score reaches 6-6, neither side has the necessary win by two condition to take the set, so now the winner is decided by a tie breaker. Unlike the game scoring described above, tie breaker scoring is just 0,1,2,3,... but you will find that which side players stand on and when to switch sides may be confusing.
If you still aren't totally sure don't worry. It takes a while to pick up the whole system and feel free to ask the coaches if they aren't too busy any questions you have!