When you start the game, you'll need to give your tennis player a name and an appearance. Then, you'll start your career at the very bottom, and you'll have to work diligently to eventually see your name among the top players in the world.
To do so, you'll need to do more than just train: you also need to participate in other activities to keep your player entertained and content... or even just take some time off to allow them to rest. Going to the horse races, driving go-karts, or letting loose at the casino are some of your non-tennis options.
New Star Tennis is an entertaining game, and while it may seem a little odd at first, hang in there and you're sure to have a great time.
Only the beginning of your career is playable.