Brennstoffet er for stormkjøkkenet.

Because both nouns are neuter singular definite nouns in Bokmål.

• et brennstoff = a fuel
• brennstoffet = the fuel
• et stormkjøkken = a camping stove / camp cookset
• stormkjøkkenet = the camping stove

So the ending -et is the definite article for many neuter nouns.

In Norwegian, the is usually attached to the end of the noun instead of standing in front of it.

So:

• the fuel → brennstoffet
• the camping stove → stormkjøkkenet

This is one of the biggest differences from English.
A separate word can appear as well when there is an adjective:

• det store stormkjøkkenet = the big camping stove

But with just the noun, the ending usually does the job.

Here, for means intended for, meant for, or to be used with.

So Brennstoffet er for stormkjøkkenet means that the fuel is the correct fuel for that camping stove. It does not mean because of the camping stove.

Sometimes yes, depending on the nuance.

• for often emphasizes purpose or suitability
• til often emphasizes destination, assignment, or belonging to

So:

• Brennstoffet er for stormkjøkkenet = the fuel is intended for the camping stove
• Brennstoffet er til stormkjøkkenet = the fuel is for the camping stove, in the sense that it goes with it or is meant to be used with it

In real life, both can be possible, but for works well when talking about compatibility or intended use.

Stormkjøkken is a compound noun:

• storm
• kjøkken = kitchen

Literally, it looks like storm kitchen, but the real meaning is a portable camping stove / camp cooking set, especially one used outdoors in windy conditions.

It is a standard Norwegian outdoor word, not a strange or poetic expression.

Because Norwegian normally writes compound nouns as one word.

So English often has:

• camping stove
• fuel bottle
• kitchen table

But Norwegian usually joins these ideas together:

• stormkjøkken
• drivstoffflaske
• kjøkkenbord

This is very normal in Norwegian, and learners need to get used to long compound words.

Yes. The definite form stormkjøkkenet means the camping stove, so it refers to a specific one that the speaker and listener can identify.

If you were speaking more generally, you would probably use an indefinite or more general expression instead.

Compare:

• Brennstoffet er for stormkjøkkenet = the fuel is for the camping stove
• Brennstoff for stormkjøkken = fuel for camping stoves

So the sentence you have is about a particular stove, not the category in general.

Because mass nouns can still be definite in Norwegian, just as they can in English.

Compare English:

• Fuel is expensive.
• The fuel is expensive.

The second one refers to a specific fuel, or the fuel already being discussed.

Norwegian works the same way:

• Brennstoff er dyrt. = fuel is expensive
• Brennstoffet er dyrt. = the fuel is expensive

So brennstoffet does not mean one single unit of fuel. It just means the specific fuel in question.

The kj sound is tricky for English speakers. Traditionally, it is a soft sound that does not really exist in standard English.

A rough learner-friendly idea:

• kjø sounds a bit like a soft hy sound said with rounded lips

Also:

• ø is not like regular English o
• it is closer to the vowel in French peur or German schön

You do not need perfect pronunciation immediately, but it helps to know that kj is meant to sound different from sj in careful Norwegian speech, even though some speakers merge them.

The sentence follows a very common Norwegian pattern:

• Brennstoffet = subject
• er = verb
• for stormkjøkkenet = prepositional phrase

So it is simply:

Subject + verb + complement

That is why it looks quite close to English:

• The fuel is for the camping stove.
• Brennstoffet er for stormkjøkkenet.

The main differences are the definite endings and the compound noun.