Hún biður mig að undirstrika mikilvægustu orðin og lesa síðan textann aftur.

Biður is the 3rd person singular present form of the verb að biðja (to ask, to request, to ask for).

So:

• ég bið = I ask
• þú biður = you ask
• hún biður = she asks

Because the subject is hún (she), Icelandic uses biður.

This verb is a little irregular, so it is worth learning its forms separately.

Because mig is the accusative form of ég (I / me).

The verb pattern here is:

• að biðja einhvern að gera eitthvað
• to ask someone to do something

So in the sentence:

• Hún biður mig ...
• She asks me ...

The person being asked takes the accusative case, so you need mig, not ég.

Compare:

• ég = I
• mig = me

This follows a very common Icelandic structure:

• biðja + accusative person + að + infinitive
• ask + someone + to + verb

So:

• Hún biður mig að undirstrika ...
• literally: She asks me to underline ...

Then another infinitive is added with og:

• ... og lesa síðan textann aftur
• ... and then read the text again

So the full structure is:

• Hún biður mig
• að undirstrika mikilvægustu orðin
• og lesa síðan textann aftur

In Icelandic, when two infinitives are linked by og (and), it is very common to use að only once if both verbs belong to the same structure.

So:

• að undirstrika ... og lesa ...

means:

• to underline ... and read ...

Repeating að is usually unnecessary here.

This works much like English:

• She asks me to underline the words and read the text again

You would not normally say:

• She asks me to underline the words and to read the text again

Even though that is possible in English, the shorter version is more natural in both languages here.

Undirstrika is the infinitive form of the verb, meaning to underline.

It appears after að, which often marks the infinitive:

• að undirstrika = to underline

In this sentence, it depends on biður mig að ..., so it tells what she is asking me to do.

This means the most important words.

Here is how it works:

• mikilvægur = important
• mikilvægari = more important
• mikilvægastur = most important

In the sentence, the adjective appears as mikilvægustu, because it has to agree with orðin.

Why that ending?

Orðin is:

• neuter plural
• definite = the words

When an adjective comes before a definite noun in Icelandic, it usually takes the weak form.
So instead of a form like mikilvægust, you get mikilvægustu.

So:

• mikilvægustu orðin = the most important words

Orðin is the definite form of orð (word).

• orð = word / words
• orðin = the words

A few useful points:

• orð is a neuter noun
• its singular and plural can look similar, so context matters
• here orðin is clearly plural definite

In this sentence it is the object of undirstrika, so the meaning is the words being underlined.

Because for many neuter nouns in Icelandic, the nominative and accusative forms are the same.

So with orðin, the form itself does not tell you whether it is subject or object.
You understand its role from the sentence structure:

• Hún is the subject
• biður is the verb
• mig að undirstrika mikilvægustu orðin tells what she asks me to do

So orðin is understood as the object of undirstrika, even though its form matches nominative as well.

Síðan means then, after that, or sometimes afterwards.

Here it connects the two actions in order:

1. underline the most important words
2. then read the text again

So:

• lesa síðan textann aftur
• then read the text again

It helps show sequence.

Icelandic word order is fairly flexible, especially with adverbs like síðan.

Here:

• og lesa síðan textann aftur

is a natural way to say:

• and then read the text again

The adverb síðan often appears near the verb or before the object.
This placement sounds normal and idiomatic.

You may also see adverbs in slightly different positions in other sentences, depending on style and emphasis.

Textann is the accusative singular definite form of texti (text).

So:

• texti = a text
• textann = the text

It is in the accusative because it is the object of lesa (to read):

• lesa textann = read the text

Aftur means again.

So:

• lesa textann aftur = read the text again

Putting aftur at the end is very natural in Icelandic. It modifies the whole action of reading.

The sentence is telling you to read the text one more time, after underlining the important words.

Not always. Að biðja can mean different things depending on the context.

Common uses include:

• ask
• request
• ask for
• sometimes even pray

For example:

• biðja einhvern að koma = ask someone to come
• biðja um hjálp = ask for help

In this sentence, the meaning is clearly ask or request:

• Hún biður mig að ...
• She asks me to ...

More or less, yes:

• Hún = she
• biður = asks
• mig = me
• að undirstrika = to underline
• mikilvægustu orðin = the most important words
• og = and
• lesa = read
• síðan = then
• textann = the text
• aftur = again

A very close literal version would be:

• She asks me to underline the most important words and read then the text again.

But natural English would be:

• She asks me to underline the most important words and then read the text again.

So the Icelandic and English structures are actually quite similar here.

Yes, several very useful patterns appear here:

1. biðja einhvern að gera eitthvað
   = ask someone to do something

2. accusative pronouns after certain verbs

   • mig = me

3. definite noun + weak adjective

   • mikilvægustu orðin = the most important words

4. coordinated infinitives

   • að undirstrika ... og lesa ...

5. common adverbs of sequence and repetition

   • síðan = then
   • aftur = again

It is a very good example sentence because it combines everyday vocabulary with several important grammar patterns.