Það er ekki nóg þvottaefni eftir, svo við þurfum að fara í búð á morgun.

This is a very common Icelandic way to introduce the existence or amount of something, much like English there is or there are.

So Það er ekki nóg þvottaefni eftir is structurally like:

• There is not enough detergent left

Here, það does not literally mean a specific it. It is part of an impersonal or existential construction.

Because þvottaefni is being treated as a mass noun, the verb is singular: er.

In a normal main clause, Icelandic usually puts ekki after the finite verb.

So:

• Það er ekki...
• Við þurfum ekki...

This is the usual neutral word order.

A learner might be tempted to place ekki later, closer to the word it seems to negate, but Icelandic normally wants it right after the finite verb unless there is some special emphasis.

This is a very common learner question.

• nóg = enough, used on its own or directly with a noun
• nógu = enough, used before an adjective or adverb

So here:

• nóg þvottaefni = enough detergent

But you could say:

• nógu mikið þvottaefni = enough detergent, literally enough much detergent
• nógu vel = well enough

So nóg is correct in ekki nóg þvottaefni.

Þvottaefni is a compound noun. It is made from parts related to washing and material/substance, so its literal structure is something like washing substance.

In everyday usage, it means detergent.

It is usually treated as a mass noun, like soap or detergent in English. That is why the sentence talks about whether there is enough of it, rather than counting individual items.

Here eftir means left or remaining.

So:

• þvottaefni eftir = detergent left
• ekki nóg þvottaefni eftir = not enough detergent left

In this sentence, eftir is not really functioning like the English preposition after. It is more like an adverb meaning remaining.

This is a very common Icelandic pattern:

• Það er engin mjólk eftir = There is no milk left
• Áttu kaffi eftir? = Do you have coffee left?

Because in this kind of expression, Icelandic often places eftir after the thing that remains.

So the pattern is often:

• vera eitthvað eftir = to be something left
• eiga eitthvað eftir = to have something left

That is why þvottaefni comes first and eftir follows it.

For an English speaker, this can feel a bit like detergent left, which is actually not so different from English once you think of left as coming after the noun.

Svo here means so in the sense of therefore or as a result.

It connects the two ideas:

• there is not enough detergent left
• as a result, we need to go to the store tomorrow

So it is linking cause and result.

In this use, svo joins two main clauses, which is why the second part keeps normal main-clause word order.

The verb þurfa means to need.

In normal Icelandic, it is usually followed by:

• að + infinitive

So:

• við þurfum að fara = we need to go
• ég þarf að vinna = I need to work
• þau þurfa að kaupa mjólk = they need to buy milk

Here:

• þurfum is the present tense, first person plural
• að fara is the infinitive phrase meaning to go

English speakers sometimes expect the infinitive marker to disappear after a verb like need, but Icelandic keeps að here.

Icelandic often uses fara í búð for go to the store.

Literally, it is closer to go into a shop/store, but in everyday Icelandic this is just the normal way to express the idea.

So although English says to the store, Icelandic usually says í búð.

A useful contrast is:

• fara í búð = go to the store
• vera í búð = be in the store

That is a very common Icelandic pattern with places.

Without the article, í búð sounds general and idiomatic. It often means going to a shop or to the store in the everyday sense, without stressing exactly which one.

With the article:

• í búðina = to the specific store

So the difference is roughly:

• fara í búð = go to the store, go shopping for necessities
• fara í búðina = go to the particular store that both speaker and listener have in mind

In this sentence, the general version is the most natural.

Á morgun is simply the standard Icelandic expression for tomorrow.

It is a fixed time expression, and learners just have to get used to it as a set phrase.

Other time expressions in Icelandic also use prepositions in ways that do not match English exactly, so this is a good example of something to learn as a chunk:

• á morgun = tomorrow
• í gær = yesterday
• á mánudag = on Monday

So even though English has a single word tomorrow, Icelandic uses the phrase á morgun.

Yes, some parts can move, but Icelandic main clauses usually follow the verb-second rule.

For example, you can move á morgun to the front:

• Á morgun þurfum við að fara í búð

That is correct.

But you would not normally say:

• Á morgun við þurfum að fara í búð

because after a fronted element, the finite verb usually comes next.

So the original sentence is neutral and natural, but Icelandic does allow rearranging parts for emphasis, as long as the verb-second pattern is respected.