We don't have two different words for "his," in English, so let's use first person as an example: My shoe (mi zapato) vs. The shoe is mine (el Zapato es mío)
Su is to mi what suyo is to mío: His shoe (Su zapato) vs. The shoe is his (El zapato es el suyo)
"Él zapato" means "He shoe", which doesn't make much sense. You probably mean "Su zapato", i.e. "His shoe". If "su" is not an available answer, try "El zapato de él" which literally means "The shoe of him". It's a roundabout way of saying the same thing.