There are 4 forms of nouns in Norwegian: 1) singular indefinite, preceded by a gendered indefinite article, 2) singular definite, with the definite article following masculine and neuter nouns but replacing the indefinite article for feminine nouns, 3) plural indefinite, formed by adding "-er" to most nouns, and 4) plural definite, formed by adding "-ene" to the noun. Irregular plural forms do exist.

1. Notes on Nouns

2. There are 4 forms of nouns:
1. Singular Indefinite (M, F, N)
The noun is preceded by the gendered
indefinite article:
A boy | En gutt (m)
A book | Ei bok (f)
A heart | Et hjerte (n)

3. There are 4 forms of nouns:
2a. Singular Definite (M, N)
The noun is followed by the gendered definite
article:
The boy | Gutten (m)
The heart | Hjertet (n)
So if you think about it literally it's kind of like
the "the" is added to the back of the noun,
instead of the front. Gutten = Boythe.

4. There are 4 forms of nouns:
2b. Singular Definite (F)
The noun is not followed by "ei." Instead it is
followed by an "a."
The book | Boka
Should you choose to learn feminine words as
common, you could take the masculine suffix.
The book | Boken

5. There are 4 forms of nouns:
3. Plural Indefinite (M, N, F)
This starts getting easy. Most nouns are just
followed by "-er."
Boys | Gutter (m)
Souls | Sjeler (f)
Hearts | Hjerter (n)
Some nouns are irregular for no rhyme or
reason. Books becomes Bøker. Watch out!

6. There are 4 forms of nouns:
4. Plural definite (M, N, F)
The noun is followed by "-ene."
The boys - Guttene (m)
The souls - Sjelene (f)
The hearts - Hjertene (n)
(The books - Bøkene [f])