NOUNS ARE INTRODUCED BY A DEFINITE ARTICLE WHEN YOU ARE SPEAKING ABOUT A SPECIFIC ITEM.  IN ENGLISH, "THE" IS USED TO INTRODUCE NOUNS: THE BOOK; THE CHAIR; THE DESKS

Spanish Definite Articles

Gender and Number English Equivalent

El Masculine Singular The

La Feminine Singular The

Los Masculine Plural The

Las Feminine Plural The

INDEFINITE ARTICLES ALSO INTRODUCE NOUNS, BUT THEY ARE NOT AS SPECIFIC.  IN ENGLISH, "A“,"AN" , “SOME” ARE INDEFINITE ARTICLES: A BOOK; A CHAIR; SOME DESKS

Spanish Indefinite Articles

Gender and Number English Equivalent

Un Masculine Singular A (An)

Una Feminine Singular A (An)

Unos Masculine Plural Some

Unas Feminine Plural Some

Articles are a good way to determine what gender a noun is, especially if it is a noun that might be an exception to the "gender rule."  Get into the habit of learning the definite article along with the noun when learning new vocabulary - that way you're never in doubt as to whether that thing is masculine or feminine.

In Spanish, the definite and indefinite article must agree with the gender and number of the noun. In this respect, articles act like adjectives - everything matches and agrees with the noun that it modifies.