Ég set sellerí og hvítkál í skálina.

Setja is the infinitive, the basic dictionary form meaning to put / to place / to set.

In the sentence, set is the present tense form used with ég:

• ég set = I put
• þú setur = you put
• hann/hún/það setur = he/she/it puts

So Ég set sellerí og hvítkál í skálina uses the finite verb form, not the infinitive.

Because í can take different cases depending on meaning:

• accusative when there is movement into something
• dative when something is already in something

Here, the action is moving the celery and cabbage into the bowl, so Icelandic uses accusative:

• í skálina = into the bowl

This is a very important Icelandic pattern:

• í skálina = into the bowl, movement toward the inside
• í skálinni = in the bowl, location inside it

So:

• Ég set sellerí og hvítkál í skálina = I put celery and cabbage into the bowl
• Selleríið er í skálinni = The celery is in the bowl

Same preposition, different case, different meaning.

Skálina comes from skál, which means bowl.

Here it is:

• skál = a bowl
• skálina = the bowl, accusative singular

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

So skálina is roughly:

• skál
  • definite ending = the bowl

Because it follows í in a motion meaning, it appears in the accusative form.

They are the direct objects of set, so grammatically they are in the accusative.

However, many Icelandic nouns do not show a visible change between nominative and accusative in this kind of form, especially neuter nouns. That is what is happening here:

• sellerí
• hvítkál

So even though they function as objects, their forms stay the same.

Because the sentence is talking about the ingredients in a general, indefinite way:

• sellerí og hvítkál = celery and cabbage

This is very natural when talking about food, ingredients, or substances.

If you meant specific known items, you could use definite forms such as:

• selleríið
• hvítkálið

That would mean something more like the celery and the cabbage.

Yes. This is a very natural, neutral word order:

• Ég = subject
• set = verb
• sellerí og hvítkál = object
• í skálina = prepositional phrase

So the structure is basically:

subject + verb + object + place/direction phrase

Icelandic word order can change for emphasis, but this sentence is the straightforward default way to say it.

For example, you could also front the destination for emphasis:

• Í skálina set ég sellerí og hvítkál

But the original version is the most neutral.

Usually, no. In normal Icelandic, subject pronouns are generally expressed.

So:

• Ég set ... = normal
• leaving out ég would usually sound incomplete unless the context is very special

Also, set is not uniquely a first-person form in all contexts, so keeping ég makes the subject clear.

Yes, setja is a very common verb for put, place, or set something somewhere.

In a sentence like this, where you are placing ingredients into a bowl, setja is a perfectly natural choice.

Depending on context, Icelandic can also use other verbs for putting things somewhere, but setja is one of the main everyday verbs learners should know.