Katten sover oppå sofaen.

Because katten is the definite form of katt.

• katt = a cat
• katten = the cat

In Norwegian, the definite article is often added to the end of the noun instead of being a separate word at the front.

So:

• en katt = a cat
• katten = the cat

This is very different from English, where the is a separate word.

For the same reason: sofaen is the definite form.

• en sofa = a sofa
• sofaen = the sofa

The ending -en marks definiteness for many masculine nouns. So both katten and sofaen mean the cat and the sofa.

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

In this sentence:

• katten = the cat
• sofaen = the sofa

So Norwegian does not need a separate word like English the here.

Sover is the present tense of the verb å sove (to sleep).

• å sove = to sleep
• sover = sleep / is sleeping

In Norwegian, the present tense is often used where English might use either:

• sleeps
• is sleeping

So Katten sover can match English The cat sleeps or The cat is sleeping, depending on context.

Because Norwegian usually does not form the present continuous the way English does.

English often says:

• The cat is sleeping

But Norwegian normally just uses the simple present:

• Katten sover

So the idea of an action happening right now is often understood from context, without needing a separate verb like is.

Oppå means on top of. It is more specific than på, which often just means on.

So:

• på sofaen = on the sofa
• oppå sofaen = on top of the sofa

With oppå, there is often a stronger sense of physical position on the upper surface.

In real speech, Norwegian speakers sometimes use på where English might say on or on top of, but oppå adds extra clarity.

This sentence has very normal Norwegian word order:

• Katten = subject
• sover = verb
• oppå sofaen = place expression

So the pattern is:

Subject + Verb + Place

That is the standard order in a simple statement.

Yes. That is also natural.

The difference is mainly this:

• på sofaen = on the sofa
• oppå sofaen = on top of the sofa

In many situations, på sofaen is the more usual everyday phrasing if you simply mean the cat is on the couch. Oppå sofaen can sound a bit more specific or emphatic.

Because they are usually treated as common-gender nouns in Bokmål, and common-gender nouns often take:

• en in the indefinite singular
• -en in the definite singular

So:

• en katt → katten
• en sofa → sofaen

This is one of the basic noun patterns in Norwegian.

A helpful breakdown is:

• Katten = the-cat
• sover = sleeps / is sleeping
• oppå = on top of
• sofaen = the-sofa

So the structure is very compact compared with English, because Norwegian packs the into the noun itself.

A simple learner-friendly approximation is:

• oppå ≈ OP-poh

A few useful notes:

• the å sounds like the vowel in British English law or more for many learners
• the stress is usually on the first syllable: OP-på

You may also hear slight variation depending on dialect, but that approximation is a good start.