Articles

Singular countable nouns mentioned for the first time.

Ex: A black cat was found in my house.

Jobs

Ex: His mom is a doctor.

Don't use it with uncountable nouns

Ex: Knowledge makes people powerful.

Things already mentioned before; clear reference.

Ex: The English teacher is from Italy.

Particular things

Ex: The music my mom likes is boring.

Unique things

Ex: The sun

Nationalities.

Ex: The French; The Brazilian

Superlatives; ordinal numbers

Ex: The best / The first

Common expressions

Ex: The world; On the other hand

In general, in plural.

Ex: Teachers are not paid enough.

Common expressions

Ex: In + bed/hospital/prison/school

Ex: At + home/university/work