It is understood that you need to upgrade your car every time you enter a race. That is the bible of the sports. Actually, it is not a must, but you need to do it if you want to compete with the best. Competing with the best of the best really is expensive, but the price is really high.
This game allows you to race all over the world. You won't see other cars besides you racing, but you will need to drive as fast as you can and get to the finish line in the least possible time. Grab some coins along the way as you can use it to upgrade your car later. You will learn more as you move from one level to another.