Learn Hardcore Icelandic: Sagan er löng.

Most Icelandic nouns ending in -a are feminine, but there are exceptions. You’ll learn them over time, and every noun in a dictionary is marked with its gender. As a general guideline:

-a → usually feminine (e.g. saga, hús is an exception)
-ur → often masculine (e.g. stallur)
-i/-j/-t → often neuter (e.g. barn, hálft)

What form is löng? Why isn’t it langur?

langur is the dictionary (masculine) form “long.” Adjectives in Icelandic change to match the gender, number and case of the noun they describe.

löng = feminine singular nominative (strong/indefinite) form of langur, agreeing with saga (feminine, singular, nominative).

Why is the adjective löng not in a “definite” form, since sagan is definite?

Adjectives used predicatively (i.e. after a linking verb like er) always take the strong/indefinite declension, regardless of the noun’s definiteness. Only attributive adjectives (before the noun) show a weak/definite form when the noun is definite.

If I want to say “a long story” or “the long story” with the adjective before the noun, how would I do that?

Attributive adjective forms:

“a long story” = löng saga (indefinite, strong form)
“the long story” = löngu sagan (definite, weak form; notice löngu not löng)

What does er mean and how is it pronounced?

er is the present-tense, third-person singular of vera (“to be”), so er = “is.” It’s pronounced like the English word “air” but shorter, roughly [ɛr].

How do I pronounce the vowel ö in löng, and what about the ng cluster?

ö is a rounded front vowel [œː], similar to German ö in schön.
Final ng is typically [ŋk] (a nasal plus stop).
So löng ≈ [lœːŋk].

How do I turn Sagan er löng into a question?

Invert verb and subject:
Er sagan löng?
(“Is the story long?”)

How would I say “The story was long” instead of “is long”?

Use the past tense of vera, which is var:
Sagan var löng.
(“The story was long.”)