In Spanish, nouns (sustantivos) are either masculine (m.) or feminine (f.). Each gender has its own article.

Nouns that end in a are almost always feminine and nouns that end in o are almost always masculine.

To form the plural of a noun, add an s to the end if it ends in a vowel...

el día los días	the day the days
el amigo los amigos	the friend the friends

and an es to the end if it ends in a consonant...

el canal los canales

the canal the canals

If the noun ends in -ion, the accent is dropped for the plural form.

la nación   las naciones

the nation the nation