the, a, and an

Definite article: the

The is the definite article. It is used before a noun to refer to a specific one. 

Examples:

• Can you please hand me the green towel? (I only want the green towel.)
• I want the cherry pie. (I want a specific pie.)
• She wants the apple. (I want the specific apple you are holding.)
• I like the elephants at the zoo. (I like those elephants at that zoo.)

Indefinite articles: a/an

A and an are indefinite articles. They are used before nouns to refer to something in general.