For one player mode, use the left and right arrow keys to steer and the up arrow to go. For two player mode, control the red car the same as above, and the blue car with the 'A' key to turn left and the 'D' key to turn right, and use the 'S' key to go. In two player mode, to win the demolition derby smash into the other car as fast as you can.
I made this a long time ago. It's not the best but it's still fun. inspiration and car artwork from the book 'coding for beginners using scratch' from usborne.