Veggen er tynn.

Vegg means wall in the indefinite form.
Veggen means the wall in the definite singular form.

Norwegian often makes nouns definite by adding an ending:

• en vegg = a wall
• veggen = the wall

So in Veggen er tynn, the speaker is talking about a specific wall.

In Norwegian, the is usually built into the noun as a suffix instead of being a separate word.

So:

• vegg = wall
• veggen = the wall

This is very common in Norwegian. English uses a separate word, but Norwegian often adds the definiteness directly to the noun.

Vegg is a masculine noun in Bokmål.

Its basic forms are:

• en vegg = a wall
• veggen = the wall
• vegger = walls
• veggene = the walls

The gender matters because adjectives can change form depending on the noun they describe.

Because tynn here is a predicative adjective: it comes after er and describes the subject.

In Norwegian, predicative adjectives usually agree with gender and number, but not with definiteness in the same way as adjectives placed before nouns.

So:

• Veggen er tynn = The wall is thin
• Huset er tynt = The house is thin
• Veggene er tynne = The walls are thin

But when the adjective comes before a definite noun, you do use the definite-style form:

• den tynne veggen = the thin wall

So compare:

• veggen er tynn
• den tynne veggen

That difference is very important.

The adjective tynn changes form depending on what it describes:

• tynn for singular masculine/feminine nouns
  
  • en vegg er tynn
• tynt for singular neuter nouns
  
  • et papir er tynt
• tynne for plural
  
  • veggene er tynne

So in Veggen er tynn, tynn matches a singular non-neuter noun.

Because tynn is an adjective, not a noun.

After er, Norwegian often uses an adjective directly:

• Veggen er tynn
• Boken er gammel
• Huset er stort

You would not say er en tynn here, because that would be incomplete. If you use en, you normally need a noun after it:

• Det er en tynn vegg = It is a thin wall

But:

• Veggen er tynn = The wall is thin

Yes. This is the standard word order for a simple statement:

• subject + verb + adjective

So:

• Veggen = subject
• er = verb
• tynn = adjective

This is completely natural Norwegian word order for a basic descriptive sentence.

A rough pronunciation guide is:

• Veggen ≈ VEG-gen
• er ≈ a short air sound, often weaker in connected speech
• tynn has a vowel that does not exist in English; it is the Norwegian y sound

A rough English-style approximation could be:

• VEG-gen er tünn

A few useful notes:

• gg in veggen is pronounced as a real g sound.
• y in tynn is like saying ee while rounding your lips.
• The final nn is a clear double n sound.

So the hardest part for most English speakers is usually tynn.