Hún bíður niðri við innganginn, svo við þurfum ekki að kalla á hana.

Because the subject is hún (she), and bíður is the 3rd person singular present tense form of að bíða (to wait).

So the verb changes like this:

• ég bíð = I wait / am waiting
• þú bíður = you wait / are waiting
• hún bíður = she waits / is waiting
• við bíðum = we wait / are waiting

In this sentence, Hún bíður means she is waiting or she waits, depending on context. Icelandic often uses the simple present where English might prefer is waiting.

Icelandic does not have a separate progressive tense like English is waiting, is calling, is reading, etc.

So:

• Hún bíður can mean she waits or she is waiting
• Við þurfum ekki can mean we do not need / we are not needing, though English strongly prefers we do not need

You understand the exact sense from context. In this sentence, Hún bíður is naturally understood as She is waiting.

Niðri usually describes location: down, downstairs, down below.

Niður usually suggests movement downward: down, downwards.

So:

• Hún bíður niðri = She is waiting downstairs/down below
  → location
• Hún fer niður = She goes down
  → movement

That is a very common Icelandic distinction:

• úti = outside, outdoors
• út = out
• inni = inside
• inn = in
• uppi = up, upstairs
• upp = up
• niðri = down, downstairs
• niður = down

Not really. The two parts add slightly different information:

• niðri = down below / downstairs
• við innganginn = by the entrance

Together they mean something like:

• down by the entrance
• downstairs at the entrance
• down there by the entrance

So niðri tells you the general area, and við innganginn gives the more exact location.

Because the preposition við takes the accusative case in this meaning.

The noun is inngangur (entrance). Its definite singular forms include:

• nominative: inngangurinn
• accusative: innganginn
• dative: innganginum
• genitive: inngangsins

Since við requires the accusative here, you get:

• við innganginn = by the entrance

This is something Icelandic learners have to memorize with prepositions: many prepositions regularly require a specific case.

That is the definite article, attached to the end of the noun.

So:

• inngangur = an entrance / entrance
• innganginn = the entrance (accusative singular)

Unlike English, Icelandic usually puts the on the end of the noun rather than as a separate word.

Compare:

• hundur = dog
• hundurinn = the dog

Because this sentence uses við + accusative, the definite form becomes innganginn, not the nominative inngangurinn.

Here svo means something like:

• so
• therefore
• which means that

In this sentence:

• Hún bíður niðri við innganginn, svo við þurfum ekki að kalla á hana.

The idea is:

• She is waiting down by the entrance, so we do not need to call her.

In other contexts, svo can also mean then, and then, very, or appear in various idiomatic expressions, so its exact meaning depends on context.

Because the subject there is við (we), and þurfum is the 1st person plural present form of að þurfa (to need / have to).

For example:

• ég þarf = I need
• þú þarft = you need
• hann/hún þarf = he/she needs
• við þurfum = we need
• þið þurfið = you (plural) need
• þeir/þær þurfa = they need

So við þurfum ekki means we do not need.

Because ekki (not) usually comes after the finite verb in a normal main clause.

So:

• við þurfum ekki = we do not need
• hann kemur ekki = he is not coming
• ég skil þetta ekki = I do not understand this

That word order is very typical in Icelandic.

Because að kalla is the infinitive, to call, and þurfa is followed by an infinitive to express need to.

So:

• við þurfum að fara = we need to go
• ég þarf að borða = I need to eat
• þau þurfa að bíða = they need to wait

Here:

• við þurfum ekki að kalla á hana = we do not need to call her / call for her

In dictionary form, Icelandic infinitives normally include að, so you will usually learn the verb as að kalla, að bíða, að þurfa, etc.

Að kalla á is a common verb + preposition combination, and it means something like:

• to call to someone
• to call for someone
• to summon someone

That is different from plain að kalla, which can mean to call, to name, or to shout/call out, depending on context.

So:

• að kalla can be more general
• að kalla á einhvern specifically means calling to/for someone

In this sentence, the meaning is that they do not need to call out to her or summon her, because she is already waiting downstairs by the entrance.

Because after á in kalla á, the pronoun appears in the form required by that construction: hana.

The pronoun forms are:

• hún = she (subject form)
• hana = her (object form)

So:

• Hún bíður = She is waiting
• við köllum á hana = we call her / call to her / call for her

English also makes this distinction:

• she is waiting
• we call her

Not in this sentence. Even though á often means on, in combinations like kalla á you should learn the whole expression together.

So here:

• kalla á hana does not mean call on her in a physical or literal on sense
• it means call to her, call for her, or summon her

This is a good example of why Icelandic prepositions are often best learned as part of a verb phrase.

It does, and this sentence still follows that pattern.

Main clause 1:

• Hún bíður niðri við innganginn
• Subject first, finite verb second

Main clause 2:

• svo við þurfum ekki að kalla á hana
• After svo, you get another clause where við is first and þurfum is second

So the sentence is perfectly normal.

You would notice V2 more clearly in a sentence where something other than the subject comes first, for example:

• Niðri við innganginn bíður hún. = Down by the entrance, she is waiting.

Here the location comes first, and the finite verb bíður still comes in second position.

Yes, that is possible, and it emphasizes an ongoing action a bit more.

• Hún bíður niðri við innganginn = She is waiting down by the entrance
• Hún er að bíða niðri við innganginn = She is in the process of waiting down by the entrance / She is waiting down by the entrance

The vera að + infinitive construction can sometimes feel closer to English is waiting, is reading, is eating, etc.

But in many everyday situations, plain present tense like Hún bíður is completely natural and idiomatic.

In normal Icelandic writing, a comma before svo connecting two clauses like this is very natural and standard:

• Hún bíður niðri við innganginn, svo við þurfum ekki að kalla á hana.

The comma helps separate the two clauses and makes the cause/result relationship clearer.