Við byggjum hús.

• Við = we
• byggjum = build / are building
• hús = house or houses

So the structure is very similar to English: subject + verb + object.

Because byggja is the infinitive, meaning to build. Icelandic verbs change their form depending on the subject.

Here, the subject is við = we, so the verb has to be the 1st person plural form:

• byggja = to build
• við byggjum = we build

So byggjum is the correct finite verb form for we.

It is the present tense.

Depending on context, it can be translated in English as:

• we build
• we are building

Icelandic does not have a separate present progressive form in the same way English does. If you want to make the ongoing action especially clear, Icelandic often uses:

• Við erum að byggja hús = We are building a house / house(s)

But Við byggjum hús is still a normal present-tense sentence.

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

So:

• hús can mean a house or houses, depending on context

If you want to say the house or the houses, Icelandic usually adds the definite article to the end of the noun:

• húsið = the house
• húsin = the houses

It could be either singular or plural.

That is because hús has the same form in both singular and plural in this case. So:

• Við byggjum hús can mean We build a house
• or We build houses

Context tells you which meaning is intended.

It is in the accusative case, because it is the direct object of the verb byggja.

However, you cannot see that clearly just from the form here, because hús looks the same in:

• nominative
• accusative
• singular
• plural

This is very common with some Icelandic neuter nouns.

Hús is a neuter noun.

That matters because gender affects:

• articles
• adjectives
• some pronoun choices

For example:

• húsið = the house
• stórt hús = a big house

The adjective form stórt shows the neuter gender.

A good beginner approximation is:

• við ≈ vith, with the th of this

So the letter ð is usually pronounced like the voiced th sound in this, not like the th in thin.

You do not need to pronounce it like a hard d.

This is the normal, neutral word order: subject + verb + object.

But Icelandic is also a verb-second language in main clauses. That means if another element comes first, the finite verb usually stays in second position:

• Í dag byggjum við hús = Today we are building a house / houses

So you will often see the subject come after the verb if something else is placed first.

Here is the present indicative:

• ég byggi = I build
• þú byggir = you build
• hann / hún / það byggir = he / she / it builds
• við byggjum = we build
• þið byggið = you (plural) build
• þeir / þær / þau byggja = they build

So the sentence uses the við form: byggjum.