Katten sitter i buret.

Because Norwegian often marks definiteness by adding the article to the end of the noun.

• katt = cat
• katten = the cat

So -en here works like English the.

This is very common in Norwegian:

• hund = dog → hunden = the dog
• bil = car → bilen = the car

That is because bur is a neuter noun in Norwegian.

In Bokmål, the definite singular ending depends on the gender of the noun:

• masculine: often -en
• feminine: often -a or sometimes -en
• neuter: -et

So:

• et bur = a cage
• buret = the cage

Meanwhile:

• en katt = a cat
• katten = the cat

So the different endings reflect different grammatical genders.

The dictionary forms are:

• katt → indefinite form: en katt
• bur → indefinite form: et bur

The sentence uses the definite singular forms:

• katten = the cat
• buret = the cage

So if you were learning vocabulary, you would usually memorize:

• en katt
• et bur

In Norwegian, sitte often describes position or posture, not just the action of sitting down.

So:

• Katten sitter i buret. = The cat is sitting / is seated in the cage.

If you said Katten er i buret, that would mean:

• The cat is in the cage

That sentence is also possible, but it gives less information.
sitter specifically suggests the cat is in a sitting position or is located there in that posture.

Norwegian often uses these posture verbs where English might simply use be:

• ligger = lies / is lying
• står = stands / is standing
• sitter = sits / is sitting

sitter is the present tense of sitte.

• å sitte = to sit
• sitter = sit / is sitting

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

• jeg sitter = I am sitting
• du sitter = you are sitting
• katten sitter = the cat is sitting
• vi sitter = we are sitting

So unlike English, you do not change the verb depending on the subject.

Because Norwegian usually puts the as an ending on the noun instead of using a separate word.

So English:

• the cat
• the cage

Norwegian:

• katten
• buret

This is one of the biggest differences from English noun structure.

However, Norwegian can use an extra definite word in some situations, especially with adjectives:

• den svarte katten = the black cat

But in a simple sentence like this, the ending alone is enough:

• katten
• buret

i means in.

So:

• i buret = in the cage

It is a very common preposition:

• i huset = in the house
• i bilen = in the car
• i Norge = in Norway

In this sentence, it shows where the cat is.

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

subject + verb + adverbial/place expression

So:

• Katten = subject
• sitter = verb
• i buret = location

This matches standard English fairly closely:

• The cat
  • is sitting
    • in the cage

Norwegian main clauses usually put the finite verb in the second position, and this sentence follows that pattern naturally.

Yes. inne i can mean inside and can make the location sound a bit more explicit.

• Katten sitter i buret. = The cat is sitting in the cage.
• Katten sitter inne i buret. = The cat is sitting inside the cage.

The version with just i is completely normal and natural.
Using inne i simply adds emphasis to being physically inside.

The indefinite version would be:

En katt sitter i et bur.

That means:

• A cat is sitting in a cage.

Compare:

• Katten sitter i buret. = The cat is sitting in the cage.
• En katt sitter i et bur. = A cat is sitting in a cage.

This is a useful comparison because it shows both indefinite articles and definite endings:

• en katt → katten
• et bur → buret

A careful approximate pronunciation for an English speaker is:

KAH-ten SIT-er ee BÜ-ret

A few notes:

• tt in katten is pronounced clearly.
• sitter has a short i sound.
• u in bur is not like English oo; it is a front rounded vowel that many learners find tricky.
• The r sound varies by dialect.

If you are learning Bokmål, remember that spelling does not always tell you exactly how a word sounds, since pronunciation differs across Norway. Still, this sentence is very standard and easy to recognize in speech.