Coins are used to pay the entry fee to certain events, to build or upgrade vehicles, and to purchase boosters before a race. They are also used to purchase better quality parts from the Coin Mall.
Coupons are used to purchase parts. When you purchase with coupons you will receive a part that has a star rating between 1 to 5 Stars.
Clovers are also used to purchase parts. When you make a purchase using a clover + coupons you will increase your chance of receiving a part that has a star rating between 3 to 5 Stars.
Trophies are premium currency and can be used to purchase higher quality parts. When you purchase with trophies you are guaranteed to receive a part that has a star rating between 3 to 5 Stars.
When you use trophies in the Choro Q or KIA shop you are guaranteed to receive a part that has a star rating between 3 to 5 Stars with the chance of it being Choro Q or KIA.
Every time you use trophies to buy parts you will receive 1 Lucky Diamond. When you have 7 Lucky Diamonds, the next time you purchase with trophies will guarantee you a 4 to 5 star part.
Scout for Team Members
Trophies are also used to scout for new team members (scouting for team members gives you bonus coins).