Bipersonen sender brevet.

Because -en is the definite singular ending for many common-gender Danish nouns.

So:

• en biperson = a supporting character / a secondary person
• bipersonen = the supporting character / the secondary person

In Danish, the equivalent of English the is often added to the end of the noun instead of being a separate word.

Because brev is a neuter noun, not a common-gender noun.

Danish singular nouns usually belong to one of two genders:

• common gender → often take -en in the definite singular
• neuter → often take -et in the definite singular

So:

• et brev = a letter
• brevet = the letter

That is why the sentence has bipersonen but brevet.

In Danish, when a noun stands by itself, the is usually expressed as a suffix on the noun.

So instead of saying something like the biperson and the letter with a separate article before the noun, Danish normally says:

• bipersonen
• brevet

A separate definite article can appear in other structures, especially when an adjective is added, for example:

• den store biperson = the big supporting character
• det lange brev = the long letter

But in your sentence, the simple noun form takes the ending directly.

Sender is the present tense of the verb at sende = to send.

For many Danish verbs, the present tense ends in -r:

• at sende = to send
• sender = send / sends

Danish does not change the verb depending on the subject the way English does. So the same present-tense form is used with all persons:

• jeg sender = I send
• du sender = you send
• han/hun sender = he/she sends
• de sender = they send

So sender works for bipersonen without any extra change.

Yes. In this sentence, the word order is straightforward subject + verb + object:

• Bipersonen = subject
• sender = verb
• brevet = object

So it matches English The supporting character sends the letter.

However, Danish also follows the V2 rule in main clauses, which means the finite verb is usually in the second position. In this sentence, the subject comes first, so the result looks just like English.

For example:

• Bipersonen sender brevet.
• I dag sender bipersonen brevet. = Today, the supporting character sends the letter.

In the second sentence, the verb still stays in second position.

It is built from bi- plus person.

The element bi- often has the sense of secondary, side, or supporting. So biperson refers to a secondary or supporting person/character.

Danish commonly builds words this way, and learners often need to get used to reading them as one unit.

Here the full form is:

• biperson = an indefinite noun
• bipersonen = the definite form

So yes, it is a word built from smaller meaningful parts, which is very common in Danish.

Not in this sentence if you simply mean the supporting character sends the letter.

Normally, for a simple definite noun, Danish uses the ending on the noun:

• bipersonen
• brevet

Using den or det by itself would usually sound incomplete unless something else follows, often an adjective or a relative clause.

For example:

• den vigtige biperson = the important supporting character
• det korte brev = the short letter

So in your sentence, bipersonen sender brevet is the natural form.

You usually make a yes/no question by putting the verb first:

• Sender bipersonen brevet?

That means Is the supporting character sending the letter? / Does the supporting character send the letter?

This is a very common Danish pattern:

• statement: Bipersonen sender brevet.
• question: Sender bipersonen brevet?

You add ikke for not:

• Bipersonen sender ikke brevet.

So the order is:

• subject
• verb
• ikke
• object

This placement is very common in simple main clauses.

A rough English-friendly approximation is something like SEN-er, but not exactly.

A few useful points:

• d in sender is often very soft in normal speech
• the ending -er is often reduced, not pronounced as a strong English er
• the first syllable is the most prominent: SEN-der

If you want a rough IPA guide, it is often pronounced close to [ˈsenɐ] in careful standard pronunciation.

The exact sound may vary a little depending on accent and speaking style.

Yes, that is very important in Danish.

When learning a noun, it is best to learn it together with its article:

• en biperson
• et brev

That helps you form the definite singular correctly later:

• bipersonen
• brevet

If you only memorize the noun by itself, it is much harder to know which definite ending to use.