SINGULAR, PLURAL, AND UNCOUNT NOUNS

Common Nouns can be singular, plural, or uncount.

Examples:
What's this/that? It's an apple. It's a car. It's water.
What are these/those? They're apples. They're cars.
Never use:
It's apple. (X le falta el artículo "an") They're apple. (X apple no tiene "-s") It's a water. (X sustantivos no contables no tienen artículo "a")