if ur talking about the game called drag racer v3, then i can help. first, you have to buy nitrous from the parts shop. then you'll see 2 bars at the bottom of the screen. the brown one is your oil, keep that filled so ur car will go(lol). the other bar will probily be empty, so click on it and it says nitrous tanks filled. then the bar will be filled in with blue. check it after every couple races so u dont get caught without it.
p.s, i am happy to help if you get stuck or need help, althogh i might not be able to help much, but my email is davenkorbo@hotmail.com. the only thing i havent done on the game is play online, since the author abandoned the online thing or something, lol.