Indefinite articles: a. or.  an
definite articles: the  article zero. no article.


indefinite articles: a or an.
only used with singular nouns.
a + consonant sound.
a boy, a cat, a job.
a hospital, a house.
a US (pronounced Y) citizen

an + vowel sound
an apple, an orange
a honour (silent h), an hour, an heir, an honest person…

definite articles: the / article zero (no article)
can be used with singular and plural nouns, and common and proper nouns too

the boy, the apple…

Firstly, names of hotels and restaurants.
Use of the definite article:
Example. The Ritz. The Hilton.

if the owner’s name is contained in the name of the hotel or restaurant:
Omission of the article:
Fred’s (no article)

Secondly. Use of the definite article with plural noun in proper nouns and names of families.
The Philippines.
The Simpsons.

Omission of the article with proper nouns
William. Simpson.

Thirdly.Use of the definite article when the words Republic, States, Kingdom are contained in the name:
The United States.
The UK.
The Netherlands.

Omission of the article with countries and cities.
France.
Paris.

Fourthly. Use of the definite article with newspapers:
The Guardian.
The Daily Mail.
The Times.

Omission of the article with book titles:
Harry Potter.

Fifthly. Use of the definite article with buildings and works of art:
The Empire State Building.
The Shard.
The Gherkin.

Omission of the article for particular buildings or locations.
Westminster Abbey.
Parliament Square.
Piccadilly Circus.

Sixthly. Use of the definite article with organisations:
The United Nations.
The RSPCA.
The Red Cross.

Seventhly. Use of the definite article with ordinal numbers:
the first.
the second.
the tenth.

Eighthly. Use of the definite article with superlatives:
the best
the worst
the most interesting

Ninthly. Use of the definite article with geographical features:
The Mississippi River
The Thames
The Black Forest