Hún les flokkunarleiðbeiningarnar um bylgjupappann meðan við bíðum.

Because hún is the nominative form of she, and this noun phrase is the subject of the sentence.

The main pronoun forms are:

• hún = she (nominative)
• hana = her (accusative)
• henni = her (dative)
• hennar = her/of her (genitive)

Since she is the one doing the reading, Icelandic uses hún.

Les is the present tense, 3rd person singular form of the verb lesa (to read).

So:

• ég les = I read / am reading
• þú lest = you read
• hún les = she reads
• við lesum = we read

In this sentence, hún les means she reads / she is reading.

Yes. It is the direct object of les, so it is in the accusative.

However, for this noun, the accusative plural definite form looks the same as the nominative plural definite form, so you do not see a visible difference here.

That means:

• leiðbeiningarnar can be nominative plural definite
• and also accusative plural definite

You have to tell from the sentence structure that it is the object.

Because Icelandic very often makes compound nouns.

This word can be broken down like this:

• flokkunar- = sorting / classification
• leiðbeiningar = instructions / guidelines
• -nar = the (definite article)

So Icelandic packs the idea into one compound word rather than using several separate words.

This is extremely common in Icelandic, and long compounds are normal.

It comes from flokkun, which means sorting or classification.

In compounds, the first noun often appears in a genitive/linking form, so flokkun becomes flokkunar- before the main noun.

So flokkunarleiðbeiningar literally means something like:

• instructions of sorting
• more naturally: sorting instructions

This pattern is very common in Icelandic compounds.

The base noun is leiðbeining = instruction / guidance.

Its plural is leiðbeiningar = instructions / guidelines.

That is natural here because a set of instructions is usually talked about in the plural. English does this too quite often.

The ending -nar is the definite article attached to the noun, so:

• leiðbeiningar = instructions
• leiðbeiningarnar = the instructions

In Icelandic, the is usually attached to the end of the noun rather than written as a separate word.

Because the preposition um takes the accusative case here.

The noun is bylgjupappi (corrugated cardboard), and its accusative singular definite form is bylgjupappann.

So the breakdown is:

• bylgjupappi = corrugated cardboard
• bylgjupappann = the corrugated cardboard (accusative singular)

The ending -ann includes the definite article and the case ending.

Here it means about / concerning.

So leiðbeiningarnar um bylgjupappann means the instructions about the corrugated cardboard.

The preposition um can also mean around, depending on context, but in this sentence the meaning is clearly about.

Meðan means while and introduces a clause.

Then:

• við = we
• bíðum = wait / are waiting

So meðan við bíðum means while we wait or while we are waiting.

The verb bíðum is the 1st person plural present of bíða (to wait).

Yes. The sentence as given is completely natural, but you could also put the meðan clause first:

Meðan við bíðum les hún flokkunarleiðbeiningarnar um bylgjupappann.

That is also grammatical.

A useful thing to notice is that Icelandic usually keeps the finite verb early in the main clause. So when the meðan clause comes first, the main clause begins les hún, not hún les.

That is part of the normal Icelandic word-order system.