Using "mi" does show possession in Spanish, such as "mi carro" is "my car". In Spanish, "me" is an [in]direct object pronoun, and thus when someone says "me gusta" they are saying (since "gustar" means "to be pleasing to") "it is pleasing to me". "Me gusta su carro" means "your car is pleasing to me" or "I like your car". It is different in English. To say "I like" in Spanish is to use, "me gusta[n]" because that is how it is expressed in Spanish. Hope that helped!

English: I like the car. Spanish: The car is pleasing to me. Me gusta el carro English: I like chocolate Spanish: Chocolate pleases me. Me gusta el chocolate. Note: English: I like the three dogs in the window. Spanish: The three dogs in the window please me (Me gustAN los tres perros en la ventana) English: I like the cars in the parking lot. Spanish: The three cards in the parking lot please me (Me gustAN los carros en el aparcamiento) Since the cars are doing the pleasing it's gustan Since the dogs are doing the pleasing, it's gustan But when it's a car doing the pleasing, it's gusta or when it's a dog doing the pleasing, it's gusta. Google: "verbs like gustar"