How to form the plural form of a Spanish noun depends on its ending. There are several different endings:

Nouns ending in a vowel get the ending –s:

• perro – perros (dog – dogs)
• escuela – escuelas (school – schools)

Nouns ending in a consonant have the ending –es:

• español – españoles (Spanish person – Spanish people)
• doctor – doctores (doctor – doctors)

Nouns ending in –z have it changed into c when the plural –es is added:

• cruz – cruces (cross – crosses)
• voz – voces (voice – voices)

Nouns ending in –ión or –és lose the accent mark when the plural –es is added:

• acción – acciones (action – actions)
• francés – franceses (French person – French people)

In some nouns, mostly compounds and days of the week, only the article changes: 

• el lunes – los lunes (Monday – Mondays)
• el paraguas – los paraguas (umbrella – umbrellas)
• el rascacielos – los rascacielos (skyscraper – skyscrapers)

Uncountable Nouns

Uncountable nouns, or in other words matter or abstract words, are not inflected according to the gender and number of the word, because they cannot be counted. With these words, the definite singular article is generally used:

• la amistad (friendship)
• la libertad (freedom)

Note that the singular indefinite article can be used with an uncountable noun if the noun is described by an adjective:

• una amistad importante (an important friendship)

La amistad entre Ana y Belén ha crecido con el paso de los años. Es una amistad importante.

The friendship between Ana and Belén has grown over the years. It is an important friendship.

Note the use of articles and the differences in the meaning of sentences with uncountable nouns in the following cases:

Tomo café. 

I’ll have coffee.

Tomo un café.

I’ll have a coffee. 

Tomo el café.

I’ll have the coffee.