When you "Buy Parts", make a purchase in the shop or in the coin mall, you will always receive parts. Parts can be built into a car or kept as spare parts to upgrade your other vehicles.
The icon below represents "Parts" for a car:
Parts have a silver border with a metal plate in the top left hand corner. Parts have a star rating of 1 to 5 (5 being the highest and represented by a big gold star - as above) and the number in the top right hand corner tells you how many of these parts you have.
The icon below represents "Parts" that can be built into a car (these parts would build a "Touring" car):
N.B. - You can only build cars that you don't already own!
Parts that have a blue icon with a spanner and screw driver in the bottom right hand corner can be built into the car displayed on the icon.
The icon below represents a "Car"
Cars that have been built have a stripe down the left hand side of the icon and a fuel gauge below the car.