Gender
Nouns have two genders, masculine and feminine. Some nouns (professions, persons, animals) have both masculine and feminine form (E.g. a amiga and o amigo, a irmã (sister), o irmão (brother)).
Indefinite
masculine feminine singular um (carro) uma (casa) plural (alg)uns (carros) (alg)umas (casas)
In theory indefinite plural form has article, but in practise the plural is just the noun alone. (Alg)uns or (alg)umas can be used to emphasize the meaning "some". So this table in practise would look like this:
masculine feminine singular um (carro) uma (casa) plural (carros) (casas)
Indefinite article merges with with de and em prepositions.
Definite
masculine feminine singular o (carro) a (casa) plural os (carros) as (casas)
Definite article merges with a, de, em and por prepositions.
From:https://www.dbfei.com/Article/putaoyayu/201311/8416.html