Hún setur alltaf sólkrem á húðina áður en hún fer út í hádegissólina.

Setur is the 3rd person singular present form of the verb setja (to put, place, apply).

• að setja = to put / to apply
• hún setur = she puts / she applies

So the sentence starts with Hún setur... because the subject is hún (she), and Icelandic verbs have to agree with that subject in person and number.

In Icelandic, setja often literally means put or place, but it is also commonly used in contexts where English would say apply.

So:

• setja sólkrem á húðina = literally put sunscreen on the skin
• natural English: apply sunscreen to the skin

This is a very normal way to express that idea in Icelandic.

In Icelandic, adverbs like alltaf (always) often come after the finite verb in a main clause.

So:

• Hún setur alltaf sólkrem...

is the normal word order.

English also often does something similar:

• She always puts on sunscreen

But Icelandic word order is more strongly tied to the rule that the finite verb comes early in the clause.

Sólkrem means sunscreen or sun cream. It is a neuter noun.

In this sentence, it appears without the definite article, so it means sunscreen in a general sense, not the sunscreen.

So:

• sólkrem = sunscreen
• not sólkremið = the sunscreen

That is natural here, because English also usually says she puts on sunscreen, not necessarily the sunscreen.

This is about case after the preposition á.

The preposition á can take:

• accusative when there is movement onto something
• dative when something is already on something

Here, the idea is putting sunscreen onto the skin, so Icelandic uses the accusative:

• á húðina = onto the skin

Compare:

• Sólkremið er á húðinni. = The sunscreen is on the skin.
  Here it is a location, so dative is used: á húðinni.

So the sentence uses á húðina because it describes an action directed onto the skin.

The -ina is the suffixed definite article plus the case ending.

Icelandic usually puts the at the end of the noun, not as a separate word like English.

• húð = skin
• húðin = the skin (nominative)
• húðina = the skin (accusative)

So á húðina means onto the skin.

Yes, in context it naturally means her skin, even though Icelandic does not use a possessive word here.

Because the subject is she, and we are talking about applying sunscreen, á húðina is understood as onto her skin.

This is very common in Icelandic. English often uses a possessive:

• She applies sunscreen to her skin

But Icelandic may simply use the definite noun:

• á húðina = onto the skin

The meaning is still clear from context.

Áður en means before in the sense of before something happens.

It introduces a subordinate clause:

• áður en hún fer út í hádegissólina
• before she goes out into the midday sun

So:

• áður = earlier / before
• en = than / when introducing this kind of clause

Together, áður en is a fixed expression meaning before.

Fer is the 3rd person singular present form of fara (to go).

• að fara = to go
• hún fer = she goes

So in the clause áður en hún fer..., the verb has to match hún.

In this sentence, hún is repeated because the second part is a full subordinate clause:

• áður en hún fer út...

Icelandic normally does not drop subject pronouns the way some languages do. So you usually need to say the subject again.

That makes the structure clear:

• She applies sunscreen ... before she goes out...

Út means out, but út í means something more like out into.

So:

• fer út = goes out
• fer út í hádegissólina = goes out into the midday sun

The í adds the destination or environment she is going into.

This is another case choice after a preposition.

The preposition í can take:

• accusative for movement into
• dative for location in

Here she is going out into the midday sun, so Icelandic uses the accusative:

• í hádegissólina = into the midday sun

If it were describing location instead, you would expect dative.

Hádegissólina is a compound noun.

It is made from:

• hádegi = noon / midday
• sól = sun

So:

• hádegissól = midday sun / noon sun
• hádegissólina = the midday sun (accusative definite)

This kind of compound noun is extremely common in Icelandic.

The definite form makes the phrase sound like a specific, known situation: the midday sun.

In English, we also often say:

• before she goes out into the midday sun

rather than just into midday sun.

So Icelandic uses:

• hádegissólina = the midday sun

with the suffixed definite article.

This sentence is natural, but Icelandic also often uses a reflexive phrase such as:

• Hún setur á sig sólkrem.

That literally means She puts sunscreen on herself, but in natural English it is just She puts on sunscreen.

The version in your sentence is a bit more explicit because it mentions the skin directly:

• setur sólkrem á húðina = applies sunscreen to the skin

Both are understandable and natural, depending on style and emphasis.

Yes. A learner should notice that the sentence has two parts:

1. Main clause
   Hún setur alltaf sólkrem á húðina
2. Subordinate clause introduced by áður en
   áður en hún fer út í hádegissólina

So the full structure is:

• She always applies sunscreen to her skin
• before she goes out into the midday sun

This is a very common Icelandic pattern: a main clause followed by a time clause introduced by áður en.