Við notum samtengingu til að tengja aðalsetningu og aukasetningu.

It breaks down like this:

• Við = subject, we
• notum = finite verb, use
• samtengingu = direct object, a conjunction
• til að tengja = purpose phrase, to / in order to connect
• aðalsetningu og aukasetningu = a main clause and a subordinate clause

So the overall pattern is:

Subject + verb + object + purpose phrase

Notum is the 1st person plural present tense of nota, meaning to use.

So:

• ég nota = I use
• við notum = we use

That is why við notum means we use.

Yes, notum already tells you the subject is we, but Icelandic normally still includes the subject pronoun in a full sentence.

So við notum is the normal, natural way to say we use.

Icelandic is not like Spanish or Italian, where the subject pronoun is often dropped. In Icelandic, pronouns are usually expressed unless there is a special stylistic reason not to.

Til að introduces a purpose: it means to or in order to.

So:

• til að tengja = to connect / in order to connect

In English, we often just say to connect, but Icelandic commonly uses til að + infinitive to show purpose clearly.

Because it comes after til að.

After til að, Icelandic uses the infinitive form of the verb:

• til að tengja = to connect
• til að læra = to learn
• til að skrifa = to write

The dictionary form of the verb is tengja.

They are all in the accusative singular, because they are functioning as direct objects.

• notum samtengingu = use a conjunction
• tengja aðalsetningu og aukasetningu = connect a main clause and a subordinate clause

The dictionary forms are:

• samtenging
• aðalsetning
• aukasetning

These are feminine nouns, and many feminine nouns of this type change to -u in the accusative singular.

Because Icelandic does not have an indefinite article like English a/an.

So Icelandic often just uses the noun by itself:

• samtenging can mean conjunction or a conjunction, depending on context

Here, English needs a conjunction, but Icelandic does not add a separate word for a.

Here are the main dictionary forms:

• við = we
• nota = to use
• samtenging = conjunction
• tengja = to connect
• aðalsetning = main clause
• aukasetning = subordinate clause

This is useful because the words in the sentence are not always in their dictionary form:

• notum comes from nota
• samtengingu comes from samtenging
• aðalsetningu comes from aðalsetning
• aukasetningu comes from aukasetning

These are grammar terms:

• aðalsetning = main clause
  A clause that can stand on its own.

• aukasetning = subordinate clause
  A clause that depends on another clause.

So the sentence is saying that a conjunction is used to connect those two kinds of clauses.

Here, og connects the two nouns:

• aðalsetningu
• aukasetningu

So it means and in the simple sense of joining two items in a list.

It does not mean that this whole sentence itself contains a main clause and a subordinate clause. The sentence is just talking about those grammar concepts.

Yes, Icelandic word order is somewhat flexible, but the version here is the most neutral and natural.

The sentence starts with:

• Við notum ... = We use ...

You could move another element to the front for emphasis, for example:

• Samtengingu notum við ...

That would emphasize conjunction more. But the original sentence is the plain, standard order you would usually learn first.

Because the sentence is speaking in a general instructional way:

• a main clause
• a subordinate clause

This is very common in grammar explanations. English does the same thing: We use a conjunction to connect a main clause and a subordinate clause.

It does not mean only one such pair exists in the language; it is just describing the pattern in general.