Serviceheftet viser kilometerstanden og årsmodellen.

Because Norwegian, like German, very often forms compound nouns by writing them as a single word.

• service = service
• hefte = booklet / booklet-like document

So servicehefte means service booklet, and serviceheftet means the service booklet.

This is very normal in Norwegian. English often uses two words where Norwegian prefers one:

• servicehefte = service booklet
• bilnøkkel = car key
• årsmodell = model year

Writing service heftet as two separate words would be incorrect.

The ending -et is the definite article attached to the noun. In Norwegian, the is usually added to the end of the noun instead of appearing as a separate word.

Here:

• et servicehefte = a service booklet
• serviceheftet = the service booklet

This happens because hefte is a neuter noun.

A quick comparison:

• en bil = a car → bilen = the car
• et hus = a house → huset = the house
• et servicehefte = a service booklet → serviceheftet = the service booklet

Viser is the present tense of å vise = to show.

So:

• å vise = to show
• viser = shows / is showing

In Norwegian, the present tense is the same for all subjects:

• jeg viser = I show
• du viser = you show
• han/hun viser = he/she shows
• serviceheftet viser = the service booklet shows

Unlike English, Norwegian verbs do not usually change depending on the person.

The ending -en is another definite ending, like English the.

So:

• kilometerstand = mileage / odometer reading
• kilometerstanden = the mileage / the odometer reading

And:

• årsmodell = model year
• årsmodellen = the model year

These nouns are treated as common gender nouns, so their definite singular form usually ends in -en.

Compare:

• en modell → modellen
• en stand → standen

Because Norwegian usually expresses definiteness by adding an ending to the noun.

So instead of saying:

• the mileage
• the model year

Norwegian says:

• kilometerstanden
• årsmodellen

This is one of the biggest differences from English. The definite article is often attached:

• en bil → bilen
• et hefte → heftet
• en modell → modellen

So in this sentence, all three nouns are definite:

• serviceheftet = the service booklet
• kilometerstanden = the mileage
• årsmodellen = the model year

It is a compound noun:

• kilometer = kilometer(s)
• stand = standing / position / reading

Together, kilometerstand means something like kilometer reading, which in natural English is often mileage or odometer reading.

Then the definite ending is added:

• kilometerstand = mileage / odometer reading
• kilometerstanden = the mileage / the odometer reading

So the structure is:

kilometer + stand + en

This kind of noun-building is very common in Norwegian.

That -s- is a very common linking element in Norwegian compounds.

The base word is:

• år = year

But in compounds, it often becomes:

• års-

So:

• årsmodell = model year
• årstall = year number / date
• årslønn = annual salary

It does not necessarily work exactly like English possession every time, even though it can feel similar to year's in English. In compounds, this -s- is just a normal way to connect the words.

So:

• år + modell → årsmodell
• årsmodell + en → årsmodellen

Yes, but it changes the feel of the sentence.

• Serviceheftet viser kilometerstanden og årsmodellen
  = the service booklet shows the mileage and the model year

• Serviceheftet viser kilometerstand og årsmodell
  = the service booklet shows mileage and model year

The version with definite forms sounds more like it refers to specific pieces of information in the booklet. The indefinite version can sound a bit more general or label-like.

In many practical contexts, both may be understandable, but the definite version is very natural when talking about the actual listed values in a specific booklet.

This is the normal Norwegian word order for a simple statement:

Subject + Verb + Object

• Serviceheftet = subject
• viser = verb
• kilometerstanden og årsmodellen = object

So it matches basic English word order quite closely:

• The service booklet shows the mileage and the model year.

Nothing unusual is happening here. It is a straightforward declarative sentence.

Yes, og means and and works very much like English and in this sentence.

It connects the two nouns:

• kilometerstanden
• årsmodellen

So:

• kilometerstanden og årsmodellen = the mileage and the model year

This is a simple coordination of two direct objects.

You usually have to learn noun gender along with each noun, although some endings and patterns can help.

In this sentence:

• et servicehefte → neuter
  definite: serviceheftet
• en kilometerstand → common gender
  definite: kilometerstanden
• en årsmodell → common gender
  definite: årsmodellen

A good habit is to learn nouns together with their article:

• et hefte
• en stand
• en modell

That makes it much easier to form the correct definite endings later.