First off, don't use words to suggest laziness (like "u" to mean "you"). It's part of GTP's Terms of Service. Second, this may be better suited for the "Questions and Answers" forum.
Now all kidding aside (maybe). I don't know how "u" make money. I don't even know who "u" is or what "u" serves in Gran Turismo 5. All I can suggest is to take advantage of the big-money Seasonal Events. Just make sure you have the proper car to compete in certain events. Tune it up if you have to and if you don't feel competitive enough.
And of course, play through the game. I heard that's a great way to make money in GT5. May want to try it out. Even if you end up losing races, at least you're making money by simply finishing races. That money will start rolling in as you start winning races and as you keep on racing. When all else fails as you're trying to make money- JUST RACE, BABY!