In Career mode you race against AI opponents in a series of 30 races. As you earn money, you spend it on repairs and upgrades to your car. Get enough cash together and you can even buy a new car. Most of the races are simple tournaments. You race 4 or 5 tracks and the purse is divided among the top finishers for all of the races.
Knockout races are a little more interesting.
You race a series of tracks and the last car to finish in each race is removed from the next competition. Whoever is left at the end takes first prize. There is also a High Stakes mode where you race against a single opponent. Whoever wins, wins the other guy's car. Definitely not for the faint-hearted.