Dørlukkeren lukker dørbladet.

Because Norwegian very often forms compound nouns by writing the parts together as one word.

• dør = door
• lukker = closer / something that closes
• dørlukker = door closer
• dørlukkeren = the door closer

And:

• dør = door
• blad = leaf / panel
• dørblad = door leaf / the moving part of a door
• dørbladet = the door leaf

This is much more normal in Norwegian than in English, where we often write similar expressions as two words.

The ending -en is the definite article attached to the noun. Instead of putting a separate word like the in front, Norwegian usually adds definiteness to the end of the noun.

• en dørlukker = a door closer
• dørlukkeren = the door closer

So -en here works like English the.

Because dørblad is a neuter noun.

In Norwegian, singular nouns commonly belong to:

• common gender: often take -en in the definite singular
• neuter gender: often take -et in the definite singular

So:

• en dørlukker → dørlukkeren
• et dørblad → dørbladet

That means:

• dørlukkeren = the door closer
• dørbladet = the door leaf

The base, or dictionary, forms are:

• en dørlukker
• et dørblad

The sentence uses the definite singular forms:

• dørlukkeren
• dørbladet

So when you look them up, you would usually search for dørlukker and dørblad.

They are related, but they are doing different jobs.

• dørlukkeren is a noun: the door closer
• lukker is a verb in the present tense: closes

So the sentence structure is:

• Dørlukkeren = subject
• lukker = verb
• dørbladet = object

Even though lukker appears inside the compound noun and also as the main verb, the grammar is different in each case.

Lukker is the present tense of å lukke.

• å lukke = to close
• lukker = closes / is closing

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

• jeg lukker = I close / am closing
• du lukker = you close
• han/hun lukker = he/she closes
• vi lukker = we close

So Norwegian does not add an extra -s only for he/she/it the way English does.

Because Norwegian usually marks definiteness with a suffix on the noun itself.

So instead of saying something like the door closer, Norwegian says:

• dørlukkeren

And instead of the door leaf, it says:

• dørbladet

A native English speaker often expects a separate article, but in Norwegian the ending often does that job.

No, this is the normal subject–verb–object order for a simple statement.

• Dørlukkeren = subject
• lukker = verb
• dørbladet = object

So the sentence is built very much like English:

• The door closer closes the door leaf.

It is a technical word. Blad can mean leaf, blade, or panel, depending on context. In dørblad, it means the actual moving part of the door — the door panel itself, not the whole doorway or frame.

So although an English speaker might first guess door blade, the intended meaning is more like:

• door leaf
• door panel
• the actual swinging/sliding part of the door

Ø is a vowel that English does not have exactly. It is somewhat similar to the vowel in certain pronunciations of bird or burn, but with rounded lips.

A few helpful points:

• dør is not pronounced like English door
• keep the tongue fairly forward
• round your lips while making the vowel

Also note:

• dørlukkeren begins with that same ø sound
• the r in dør affects the vowel quality a bit, as often happens in Norwegian

In Norwegian compounds, the main stress usually falls on the first part of the compound.

So you would normally stress:

• DØRlukkeren
• DØRbladet

That first element tells you what kind of thing it is:

• a closer related to a door
• a leaf/panel related to a door

Not in this sentence as written.

You generally do not use an indefinite article together with the suffixed definite form:

• correct: en dørlukker = a door closer
• correct: dørlukkeren = the door closer
• not correct: en dørlukkeren

Likewise:

• et dørblad = a door leaf
• dørbladet = the door leaf

You can sometimes have both a separate determiner and a definite ending in other structures, such as with adjectives, but not in the simple forms here.

It would be:

En dørlukker lukker et dørblad.

That means:

• a door closer closes a door leaf

Compare:

• Dørlukkeren lukker dørbladet. = The door closer closes the door leaf.
• En dørlukker lukker et dørblad. = A door closer closes a door leaf.

Yes, this sentence is normal Bokmål.

A Nynorsk version might differ, especially in the verb and possibly word choice, but the exact alternative would depend on style and technical vocabulary. For a learner, the important thing is that this sentence is perfectly standard in Bokmål and shows normal compound nouns and definite endings very clearly.