Hún setur smákökurnar á bökunarplötuna og hitar ofninn.

Setja is the infinitive, meaning to put / to place. In the sentence, the verb is conjugated for present tense, 3rd person singular because the subject is hún meaning she.

So:

að setja → hún setur

The same thing happens with hitar:

að hita → hún hitar

So the sentence uses finite verb forms, not infinitives.

Icelandic usually adds the definite article to the end of the noun instead of using a separate word like English the.

In this sentence:

smákökurnar = the cookies
bökunarplötuna = the baking tray
ofninn = the oven

This is very normal in Icelandic. Learners often need time to get used to the fact that definiteness is built into the noun form.

The base noun is smákaka in the singular. Its plural is smákökur.

Here, smákökurnar means the cookies. The ending -nar is part of the definite plural form.

So roughly:

smákökur = cookies
smákökurnar = the cookies

It is also the direct object of setur, so it is in the accusative, but for this noun the nominative and accusative plural look the same, so you do not see a separate accusative ending here.

This is a very common Icelandic case question.

With the preposition á:

• accusative is often used for movement toward / onto
• dative is often used for location / being on

Here, the cookies are being placed onto the tray, so Icelandic uses the accusative:

á bökunarplötuna = onto the baking tray

Compare:

Smákökurnar eru á bökunarplötunni.
The cookies are on the baking tray.

There, the cookies are already located there, so dative is used: bökunarplötunni.

The noun plata changes its stem in some inflected forms. This kind of vowel change is very common in Icelandic.

So:

plata → base form
plötu → oblique stem used in forms like the accusative/dative with endings

That is why the definite accusative singular becomes:

plötuna

So in the compound:

bökunarplata → baking tray
bökunarplötuna → the baking tray

This is something you usually just learn as part of the noun’s declension pattern.

Because ofninn is the direct object of the verb hitar.

The verb að hita takes an object in the accusative, so:

ofninn = the oven, accusative singular definite

ofninum is the dative form, which would be used in different contexts, for example after certain prepositions.

A useful thing to notice is that for many masculine nouns, the nominative singular definite and accusative singular definite are the same in form, so ofninn can look less obviously accusative than forms like ofninum.

In a cooking context, hitar ofninn often corresponds to what English would naturally say as preheats the oven.

A very literal translation is heats the oven, but in recipes or kitchen instructions, Icelandic often uses hita ofninn where English prefers preheat the oven.

So the exact English wording depends on context, but grammatically the Icelandic is straightforward: she heats the oven.

It has two coordinated verbs joined by og meaning and.

Structure:

Hún = subject
setur = first verb
smákökurnar = direct object of setur
á bökunarplötuna = destination phrase, telling where she puts them
og = and
hitar = second verb
ofninn = direct object of hitar

So the same subject, hún, applies to both actions:

• she puts the cookies onto the baking tray
• and she heats the oven

Usually, no. Icelandic normally does not drop subject pronouns the way some languages do.

So a full clause normally needs its subject:

Hún setur ...

However, in this sentence the second clause does not repeat hún:

Hún setur ... og hitar ofninn.

That is possible because the subject is the same in both parts and is easily understood. English does exactly the same kind of thing:

She puts the cookies on the tray and heats the oven.

You would not usually repeat she unless you wanted special emphasis.

Yes, but Icelandic has an important rule in main clauses: the finite verb tends to stay in second position. This is often called the V2 rule.

The sentence here has a normal, neutral order:

Hún setur smákökurnar á bökunarplötuna og hitar ofninn.

If you move another element to the front, the verb usually still comes second:

Núna setur hún smákökurnar á bökunarplötuna og hitar ofninn.
Now she puts the cookies onto the baking tray and heats the oven.

So word order is somewhat flexible, but not random.

Yes. Icelandic uses compound words very heavily.

smákökur is built from:

smá = small
kökur = cakes / cookies

So the idea is something like small cakes, which is the normal Icelandic word for cookies.

bökunarplata is also a compound:

bökunar- = baking, used as a linking/compound form
plata = plate / tray

So bökunarplata means baking tray.

Recognizing compounds is very helpful in Icelandic because many everyday words are formed this way.