Mario was part of the duo that defeated the evil King Kuppa a long time ago. Kuppa was a tyrant and he is abusing the land, but Princess Toadstool was the true ruler. When Kuppa first appeared, he immediately defeated the parents of Princess Toadstool and took the kingdom under his rule. Princess Toadstool summon Mario and Luigi to defeat the tyrant. The rest is history. That was a long time ago and only few remember the history of the mushroom kingdom. The world is peaceful now, so Mario and Luigi goes back to what they like. Luigi went back to the Human world, while Mario become a race car driver. He likes the thrill that he gets whenever he is racing in the mountains.
The idea here is to get to the finish line. Normally, you would need to do that in as fast as you can, but this game somehow doesn't have a timer, so you can finish the race in as fast or as slow as you want. You would want to grab the stars along the way for the score it gives. You mgiht think that you would have no problem with the game since it looks easy enough, especially since there are no rival or whatever in the game. Actually, the obstacles are mountain itself since you might crash if you are not careful enough.