Articles and nouns both have plural forms. See the table below for the plural forms of the articles.
If a noun ends in a vowel we add -s to make it plural.
|el libro (the book)
||los libros (the books)
|un libro (a book)
||unos libros (some books)
If a noun ends in a consonant we add -es to make it plural.
|la ciudad (the city)
||las ciudades (the cities)
|una ciudad (a city)
||unas ciudades (some cities)
There are actually some exceptions to the -es rule, but you will learn them in a later lesson.