Learn Hardcore Icelandic: Hann kaupir flík í búð.

Icelandic simply doesn’t use an indefinite article. Nouns in their indefinite form stand alone, so flík means (a) garment and búð means (a) store. To make a noun definite, Icelandic adds a suffix: flíkan = the garment, búðin = the store.

What cases are flík and búð in, and how can you tell?

In Hann kaupir flík í búð:

flík is the direct object of kaupir, so it’s in the accusative case. For strong feminine nouns the nom., acc. and dat. sing. all look like flík, but here it’s accusative because it follows the verb.
búð follows the preposition í indicating location, so it’s in the dative case. (The genitive would be búðar.)

What’s the difference between í búð, í búðinni, and í búðina?

í búð = in a store (indefinite location, dative).
í búðinni = in the store (definite location, dative; -inni = definite dative suffix).
í búðina = into the store (definite direction, accusative; -ina = definite accusative suffix).

How would you say “He bought a garment in a store” (past tense)?

Use the past form of kaupa, which is keypti:
Hann keypti flík í búð.

How would you say “He will buy a garment in a store” (future tense)?

You normally use the auxiliary mun + infinitive:
Hann mun kaupa flík í búð.
In everyday speech you can also use the present plus a time adverb, e.g. Hann kaupir flík í búð síðar (“He’s buying a garment in a store later”).

What’s the standard word order in a simple Icelandic sentence like this?

Icelandic follows a V2 rule: the finite verb comes in the second position. In Hann kaupir flík í búð the order is Subject (Hann), Verb (kaupir), Object (flík), Adverbial phrase (í búð). If you start with something else (e.g. an adverb), the verb still stays in slot two.

How do you form the plural of flík and búð, and how would you say “He buys garments in stores”?

flík (strong fem.) → plural nom./acc. flíkur
búð (strong fem.) → plural nom. búðir, plural dat. búðum (after í)
So “He buys garments in stores” is:
Hann kaupir flíkur í búðum.

How do you add an adjective, for example “new garment”, and where does it go?

Adjectives precede the noun and must agree in gender, number, and case. New is ný-. Since flík is feminine singular accusative, the adjective takes -ja: nýja flík.
Full sentence: Hann kaupir nýja flík í búð.

What is hann, and how do you say she and it in Icelandic?

hann is the 3rd person singular masculine pronoun (“he”).

“She” is hún (3rd person sing. feminine).
“It” depends on the noun’s grammatical gender: masculine nouns use hann, feminine nouns use hún, and neuter nouns use það.

Why do flík and búð look the same in nominative, accusative, and dative? Doesn’t that cause confusion?

Many Icelandic strong feminine nouns share the same form in sing. nom., acc., and dat. You rely on word order and prepositions to identify their roles: a noun right after a transitive verb is accusative; a noun after í (for location) is dative. The only distinct form is the genitive (e.g. flíkar, búðar).