Agenten ringer politiet.

Because Norwegian often puts the definite article at the end of the noun.

• agent = an agent
• agenten = the agent

So the ending -en here means the.

In Bokmål, agent is usually treated as a masculine noun, so the definite singular form is agenten.

A quick pattern:

• en agent = an agent
• agenten = the agent

In practice, many Norwegian nouns that refer to people use common masculine/feminine patterns like this.

Ringer is the present tense of the verb å ringe.

• å ringe = to call / to ring
• ringer = calls / is calling

Norwegian present tense is often made by adding -r to the infinitive:

• snakke → snakker
• bo → bor
• ringe → ringer

So Agenten ringer politiet uses the normal present tense.

Yes. Norwegian present tense often covers both ideas that English separates into:

• calls
• is calling

So Agenten ringer politiet could mean either, depending on context.

Because politiet is the definite form of politi.

• politi = police
• politiet = the police

Here the sentence is talking about the police in a specific sense, so the definite form is used.

Also, politi is a neuter noun, which is why the definite ending is -et:

• et politi (rarely used by itself in everyday speech)
• politiet = the police

Because Norwegian uses the verb å ringe directly with the person or organization being called.

English often says:

• call the police

and not necessarily call to the police

Norwegian works the same way here:

• ringe noen = call someone
• ringe politiet = call the police

So no extra preposition is needed.

The word order is the basic Norwegian pattern:

subject + verb + object

• Agenten = subject
• ringer = verb
• politiet = object

So:

• Agenten ringer politiet.
• The agent calls the police.

This is the standard order for a simple statement.

Yes. That would make it a yes/no question.

• Agenten ringer politiet. = statement
• Ringer agenten politiet? = Is the agent calling the police? / Does the agent call the police?

In Norwegian, yes/no questions are often formed by putting the verb first.

A simple learner-friendly approximation is:

po-li-TEE-et

The stress is mainly on -ti-.

A more detailed note:

• the final -et is pronounced, not silent
• Norwegian pronunciation varies somewhat by dialect, but this approximation is good enough for many learners

No. It is capitalized only because it is the first word of the sentence.

In Norwegian, nouns are not generally capitalized the way they are in German.

So in the middle of a sentence, you would normally write:

• agenten
• politiet

not Agenten or Politiet, unless there is some special reason such as a name or title.

Yes. Agent can refer to different kinds of agents depending on context, for example:

• a secret agent
• a representative or business agent
• an agent in a general sense

The sentence itself does not tell you which kind. You understand that from context.

It would be:

En agent ringer politiet.

That means An agent is calling the police or An agent calls the police.

Compare:

• En agent = an agent
• Agenten = the agent

So the original sentence is definite in both nouns:

• Agenten = the agent
• politiet = the police