The 3 articles in English are a, an and the. Sometimes no article is needed.
“A” and “an” are used for singular nouns that can be counted.
“A” is used before nouns that begin with consonant sounds.
“An” is used before nouns that begin with vowel sounds.
Use “the” when talking about things both the speaker and the listener(s) know about.
“The” is positioned before a noun when the listener(s) can easily identify which person(s) or thing(s) are being talked about.
Use “the” when the thing being talked about is the only one that exists anywhere, like the sun, the Earth, or the Eiffel Tower.
Use “the” before superlative adjectives, like “the best,” “the smallest,” etc.