From the Super Mario Wiki
The player starts with ten coins and must place a maximum of five coins on their cards (Each card has a different picture). Luigi then rolls a ball into the roulette. There are many slots in which the ball can roll in. Just like on the player's card, there are pictures in each slot. If the ball rolls into a slot that matches the picture that the player put coin(s) on, the player is rewarded with a certain amount of coins. The player also can put a coin in the lines in between two or four pictures to get a higher chance to win. However, the player is not rewarded with as many coins. The player can even put up to five coins on a picture to get a lot of coins but is less likely to win by doing so. The game ends when the player runs out of coins. If the player quits before running out of coins, then their current amount will be saved.
Guess where the ball will land on the roulette wheel. Guess correctly to win coins!
These are the pictures that can be seen on the player's card: