You're right, but "tienes" is specifically when talking about the person you are talking to. Tener = to have. Yo tengo = I have. Tú tienes = you have. Él/ella tiene = he/she has. Nosotros tenemos = we have. Ellos tienen =they have. Many verbs are conjugated similarly, but you can look up conjugation charts for any verbs you come across.
I guess I'm always going to be marked incorrect/wrong whenever the word 'carro' is involved. I will continue to say 'coche'. I think it's as real shame that coche isn't a acceptable option. I'm from a European country and I want to refresh my Spanish language skills so that I can use it in Spain specifically.
Tú is the singular INFORMAL you, and takes the singular second-person ending--in this case, tienes. Usted is the singular FORMAL you and takes the third-person ending--using the same verb for an example, it would be tiene.
As long as the context is clear and you use the correct verb-form, you can drop the pronoun--most Spanish-speakers do unless the context is unclear or they wish to emphasize the subject.