Traduccir
Su carro es viejos y Sus carros son viejos

I don't understand that this what indicate, His/Her,Their
for example : Mi carro es viejo means in english that "My car is old" like this what will be meaning for above sentences,

Ayudarme, por favor

Question

Traduccir
Su carro es viejos y Sus carros son viejos

I don't understand that this what indicate, His/Her,Their
for example : Mi carro es viejo means in english that "My car is old" like this what will be meaning for above sentences,

Ayudarme, por favor

Answer

In spanish, we make differences if it is about one thing (car = auto = carro = coche) or more than one thing (cars = autos = carros = coches).

If we are takling about one single car:

my car - mi auto 
your car - tu auto/ su auto (de usted, it is more formal)
his car - su auto (de él)
her car - su auto (de ella)
its car - su auto (de algo)
our car - nuestro auto (de nosotros / de nosotras, if we are all women)
your car - su auto (de ustedes/ de vosotros)
their car - su auto (de ellos/ de ellas)

so, "su auto" can be: your, his, her, its or their car.

If we are takling about two or more cars:

my cars - mis autos 
your cars - tus autos/ sus autos (de usted, it is more formal)
his cars - sus autos (de él)
her cars - sus autos (de ella)
its cars - sus autos (de algo)
our cars - nuestros autos (de nosotros / de nosotras, if we are all women)
your cars - sus autos (de ustedes/ de vosotros)
their cars - sus autos (de ellos/ de ellas)

so, "sus autos" can be: your, his, her, its or their cars.

I hope it can help you.

Answer

Su coche es viejo. His car is old. 
Tu coche es viejo. your car is old.
Sus coches son viejos. His cars are old (plural of the first sentence). He have two or more cars.

Answer

"Your car is old and his cars are old"