Sjåføren sjekker lastebilen.

Because -en is the usual definite ending for many masculine nouns in Norwegian. It works like English the attached to the end of the noun.

• sjåfør = driver

• sjåføren = the driver

• lastebil = truck
• lastebilen = the truck

So instead of using a separate word like the, Norwegian often adds the definite ending directly to the noun.

In Norwegian, definiteness is usually marked with a suffix on the noun rather than with a separate word.

So:

• the driver → sjåføren
• the truck → lastebilen

This is one of the biggest differences from English.
A separate determiner can appear in some other structures, especially with adjectives:

• the truck = lastebilen
• the big truck = den store lastebilen

But in your sentence, there are no adjectives, so the ending alone is enough.

The word order is the normal subject–verb–object pattern:

• Sjåføren = subject
• sjekker = verb
• lastebilen = object

So it lines up very neatly with English:

• The driver / checks / the truck

This is the most common word order in ordinary statements.

Sjekker is the present tense of the verb å sjekke (to check).

• å sjekke = to check
• sjekker = check / checks / is checking

Norwegian present tense is often formed with -er:

• å snakke → snakker
• å jobbe → jobber
• å sjekke → sjekker

So Sjåføren sjekker lastebilen can mean both:

• The driver checks the truck
• The driver is checking the truck

The exact English translation depends on context, because Norwegian usually does not distinguish those two as clearly as English does.

Yes, very often it does.

In Norwegian, the simple present can cover both a habitual action and an action happening right now, depending on context.

So Sjåføren sjekker lastebilen could mean:

• The driver checks the truck
  maybe as part of a routine

or

• The driver is checking the truck
  right now

If the speaker wants to make the ongoing action extra clear, Norwegian can use other expressions, but in everyday language the plain present tense is very common.

The dictionary forms are:

• sjåfør = driver
• å sjekke = to check
• lastebil = truck

The sentence uses inflected forms:

• sjåfør → sjåføren (the driver)
• å sjekke → sjekker (checks / is checking)
• lastebil → lastebilen (the truck)

When learning vocabulary, it is useful to separate the base form from the form used in the sentence.

Norwegian, like English, often makes compound nouns, but Norwegian usually writes them as one word.

So:

• lastebil = truck
• literally something like load-car

This is very normal in Norwegian. English sometimes uses a space where Norwegian does not.
For learners, it is a good habit to expect many Norwegian nouns to be written as single compounds.

Examples:

• sykehus = hospital
• fotballkamp = football match
• lastebil = truck

Both are normally masculine nouns in this sentence, which is why they take -en in the definite singular:

• en sjåfør → sjåføren
• en lastebil → lastebilen

In Bokmål, many nouns can also be treated differently depending on style or dialect, but -en here is completely standard and natural.

You would use the indefinite forms:

• En sjåfør sjekker en lastebil.

Compare:

• Sjåføren sjekker lastebilen. = The driver checks the truck.
• En sjåfør sjekker en lastebil. = A driver checks a truck.

So:

• en sjåfør = a driver

• sjåføren = the driver

• en lastebil = a truck
• lastebilen = the truck

A few sounds may stand out to an English speaker:

• sj in sjåføren and sjekker is pronounced like the sh sound in ship
• å in sjåføren is a vowel somewhat like the o in British hot or thought, depending on accent
• ø in sjåføren is a front rounded vowel that English does not really have, so it may take practice

A rough learner-friendly approximation might be:

• sjåføren ≈ SHAW-fø-ren
• sjekker ≈ SHEK-er

That said, exact pronunciation varies by dialect, so these are only approximations.

It can be read as perfectly natural Bokmål, and the words also look very familiar across varieties.

• sjåfør is common
• sjekker is common
• lastebilen is common

A learner does not need to worry much here: this sentence is straightforward and standard-looking. If you are studying Bokmål, you can safely learn it as a normal Bokmål sentence.

Sometimes, but not always with exactly the same feel.

• sjåfør specifically means driver/chauffeur
• fører can mean driver, but it can also have broader meanings depending on context

In everyday situations involving vehicles, sjåfør is very clear and natural.
So in this sentence, sjåføren is a good, direct choice.

Three important things:

1. Definite nouns take endings

   • sjåføren = the driver
   • lastebilen = the truck

2. The verb stays simple

   • sjekker = checks / is checking

3. The word order is very familiar

   • subject + verb + object

So although the sentence looks different from English because of the endings, its overall structure is actually quite easy to follow.