Hún þræddi þráðinn í nálina og byrjaði svo að sauma rólega.

A literal breakdown is:

• Hún = she
• þræddi = threaded
• þráðinn = the thread
• í nálina = into the needle
• og = and
• byrjaði = began / started
• svo = then
• að sauma = to sew
• rólega = calmly / gently / slowly, depending on context

So the Icelandic structure is very close to:

She threaded the thread into the needle and then began to sew calmly.

Because Icelandic uses þræða e-ð í e-ð, literally to thread something into something.

So:

• þráðurinn = the thread
• nálin = the needle

In English, we often say thread the needle, where needle feels like the main object. In Icelandic, the thing being moved is the main object: the thread is threaded into the needle.

That is a normal Icelandic way to express this idea.

Because þráðinn is the accusative form, and it is the direct object of þræddi.

Compare:

• þráðurinn = the thread in the nominative case
• þráðinn = the thread in the accusative case

The verb þræða takes a direct object, so Icelandic uses the accusative here.

Very roughly:

• Þráðurinn er langur. = The thread is long.
  Here it is the subject, so nominative.
• Hún þræddi þráðinn. = She threaded the thread.
  Here it is the object, so accusative.

Because í can take either the accusative or the dative, depending on meaning.

A very important rule is:

• motion into/to something → accusative
• location in/inside something → dative

Here the thread is being moved into the needle, so Icelandic uses the accusative:

• í nálina = into the needle

If you were describing location instead, you would use dative:

• í nálinni = in the needle

This accusative/dative contrast with í is one of the most common things learners need to get used to.

Þræddi is the past tense of the verb þræða.

Dictionary form:

• að þræða = to thread

Past tense forms include:

• ég þræddi = I threaded
• hún þræddi = she threaded

So in this sentence, þræddi means threaded.

It is a regular-looking weak verb in the past, and the -ddi ending is common in verbs of this type.

Because the second clause has the same subject, and Icelandic can omit it in a coordinated sentence, just like English often can.

So:

• Hún þræddi þráðinn í nálina og byrjaði svo að sauma rólega.

means:

• She threaded the thread into the needle and then began to sew calmly.

The understood subject of byrjaði is still hún.

You could compare this to English:

• She sat down and started reading.

We do not need to repeat she before started.

Because byrja is commonly followed by að + infinitive when it means begin/start to do something.

So:

• að byrja = to begin
• að sauma = to sew

Together:

• byrja að sauma = begin to sew

In this sentence:

• byrjaði að sauma = began to sew

This is a very common pattern in Icelandic, and learners should get used to seeing að before the infinitive after many verbs.

Here svo means something like then or after that.

In narratives, svo is often used to move the story forward:

• first she did one thing,
• svo she did the next thing.

So in this sentence, svo does not mainly mean so in the English sense of therefore. It is more like:

• then
• next
• after that

Rólega is an adverb. It describes how she sewed.

• rólegur / róleg / rólegt = calm, quiet
• rólega = calmly, quietly, gently

So:

• sauma rólega = sew calmly / gently

This is not an adjective agreeing with a noun. It is an adverb modifying the verb sauma.

Many Icelandic adverbs are formed with -lega, and this is a useful pattern to recognize.

Because Icelandic often places adverbs like this after the infinitive or verb phrase, especially in simple sentences.

So:

• að sauma rólega = to sew calmly

That word order is very natural.

Could Icelandic sometimes place adverbs elsewhere? Yes. But this position is straightforward and common, and it sounds normal in a sentence like this.

A few key pronunciation points:

• þ is like the th in thin
• ð is like the th in this
  In practice, its pronunciation can vary a bit depending on position.
• æ is roughly like the vowel in eye for many learners, though not exactly the same

So in words from this sentence:

• Hún begins with a normal h
• þræddi starts with th
• þráðinn also starts with th
• nálina has á, a long vowel
• sauma has au, another vowel combination learners need practice with

Also, Icelandic stress is usually on the first syllable of the word, so:

• HÚN
• ÞRÆD-di
• ÞRÁ-ðinn
• NÁ-li-na
• BYR-ja-ði
• SAU-ma
• RÓ-le-ga

The main dictionary forms are:

Nouns:

• þráður = thread
• nál = needle

Verbs:

• að þræða = to thread
• að byrja = to begin, start
• að sauma = to sew

Forms used in the sentence:

• þráðinn = the thread in accusative singular
• nálina = the needle in accusative singular
• þræddi = past tense of að þræða
• byrjaði = past tense of að byrja

This is a good example of how Icelandic sentences often contain forms that look quite different from the dictionary form because of case and tense.