Learn Hardcore Icelandic: Gatan fyrir framan húsið er róleg. - The street in front of the house is quiet.

In Icelandic the definite article is a suffix attached to the noun. Gata means “a street,” and when you make it definite (“the street”) for a feminine noun you add -n, yielding gatan.

How do I form the indefinite of gatan?

Drop the definite suffix. The indefinite nominative singular is simply gata, meaning “a street.”

What does fyrir framan mean, and why are there two words?

Fyrir is a preposition (“for/before”) and framan is an adverb (“in front”). Together they form the fixed prepositional phrase fyrir framan, which means “in front of.”

What case does the noun after fyrir framan take?

The prepositional phrase fyrir framan governs the accusative case. Thus the noun following it must appear in its accusative form.

Why does húsið end in -ið?

Hús is a neuter noun. In Icelandic, neuter singular definite nouns take -ið as the suffix. So “a house” is hús, and “the house” is húsið. Because it’s after fyrir framan, it’s in the accusative, but for neuter singular the accusative and nominative forms are identical.

Why is the adjective róleg not rólegur or rólegt?

Adjectives agree with the gender, number and case of the noun they describe when used predicatively (after the verb er). Gata is feminine singular, so you use the feminine form róleg. (Masculine would be rólegur, neuter rólegt.)

How would I ask “Is the street in front of the house calm?” in Icelandic?

Invert verb and subject for a yes/no question. You get:
Er gatan fyrir framan húsið róleg?

How do I say “The streets in front of the houses are calm” in Icelandic?

Use the plural forms and make subject, verb and adjective agree:
Göturnar fyrir framan húsin eru rólegar.

Could I use framan við húsið instead of fyrir framan húsið, and is there a difference?

Yes. Framan við húsið (“in front by the house”) also works and is grammatically correct, though fyrir framan is more common for “in front of.” Both take the accusative (húsið) afterward.