Fordonsskatten måste betalas i och med att bilen används.

Fordonsskatten means the vehicle tax.

It is a compound noun:

• fordon = vehicle
• skatt = tax
• fordonsskatt = vehicle tax
• fordonsskatten = the vehicle tax

A couple of things are happening here:

• Swedish very often makes one word where English uses two.
• When nouns are combined, they form a compound noun.
• The final -en makes it definite: the vehicle tax.

Also notice the extra s in fordonsskatt. That s is a linking sound that often appears in Swedish compounds.

In Swedish, the definite article is usually attached to the end of the noun.

So:

• en skatt = a tax
• skatten = the tax

And in the compound:

• en fordonsskatt = a vehicle tax
• fordonsskatten = the vehicle tax

This is very normal in Swedish. English uses a separate word (the), but Swedish often puts definiteness directly on the noun.

Because the sentence means that the tax must be paid, not that it must pay.

Compare:

• måste betala = must pay
• måste betalas = must be paid

So:

• Jag måste betala skatten = I must pay the tax.
• Skatten måste betalas = The tax must be paid.

In your sentence, fordonsskatten is the thing receiving the action, so Swedish uses the passive form betalas.

Yes. Betalas is the passive of betala.

• betala = to pay
• betalas = to be paid

Swedish often makes the passive by adding -s to the verb.

Examples:

• betala → betalas = pay → be paid
• använda → används = use → is used / are used
• sälja → säljs = sell → is sold / are sold

So måste betalas literally works like must be paid.

I och med att is a fixed expression. In this sentence it means something like:

• since
• because
• given that
• as a result of the fact that

So:

• Fordonsskatten måste betalas i och med att bilen används. = The vehicle tax must be paid since the car is being used.

Literally, i och med looks strange if you translate word by word, but you should learn i och med att as a whole expression.

It often introduces a reason or a condition that has real consequences.

Bilen means the car.

• en bil = a car
• bilen = the car

Swedish often uses the definite form when talking about a specific thing already understood from the situation. Here, it is not just any car in general, but the car being discussed.

So:

• att bilen används = that the car is used / being used

If you said en bil, it would sound less specific.

Används comes from använda, which means to use.

• använda = to use
• används = is used / are used

Again, this is the Swedish -s passive.

So:

• bilen används = the car is used / the car is being used

In this sentence, it expresses that the car is actually in use, and that is the reason the tax must be paid.

Yes. Används is present tense passive.

• använda = infinitive, to use
• använder = present active, uses / is using
• används = present passive, is used / is being used

So bilen används can mean:

• the car is used
• the car is being used

Which English version sounds best depends on context.

The sentence has two parts:

1. Fordonsskatten måste betalas = The vehicle tax must be paid

2. i och med att bilen används = since the car is used / being used

So the full structure is:

• main clause
  • reason clause

You can think of it like this:

• [The vehicle tax must be paid] [because the car is being used].

After att, Swedish usually has subordinate clause word order.

In this clause:

• att bilen används

the subject bilen comes before the verb används, which is exactly what you would expect in a subordinate clause.

If there were a sentence adverb like inte, you would see the subordinate-clause pattern more clearly:

• att bilen inte används = that the car is not used

Notice that inte comes before the verb används. That is typical subordinate clause word order in Swedish.

Yes. Depending on context, several translations are natural:

• The vehicle tax must be paid because the car is being used.
• The vehicle tax must be paid since the car is in use.
• The vehicle tax has to be paid as the car is being used.

If you want a more natural everyday English version, because or since often works best.

Yes, it sounds fairly formal or administrative.

Reasons:

• fordonsskatt is official vocabulary
• i och med att is a somewhat formal connector
• the passive structure måste betalas is common in rules, laws, and official information

In everyday speech, someone might choose simpler wording, but this sentence sounds very normal in official Swedish.