Deltageren læser bogen.

Because Danish usually makes nouns definite by adding the definite article as a suffix.

• deltager = participant
• deltageren = the participant

So instead of putting a separate word before the noun, Danish often attaches the idea of the to the end of the noun.

For the same reason: Danish commonly uses a suffixed definite article.

• bog = book
• bogen = the book

This is different from English, where the is a separate word. In Danish, the definite ending is usually attached directly to the noun in simple cases like this.

Because both deltager and bog are common-gender nouns, and in the singular definite form, common-gender nouns usually take -en.

So:

• en deltager = a participant

• deltageren = the participant

• en bog = a book
• bogen = the book

If a noun were neuter gender, it would often take -et instead in the definite singular.

The word order is:

Subject + verb + object

• Deltageren = subject
• læser = verb
• bogen = object

So this sentence follows a pattern very similar to normal English word order:

The participant reads the book.

Læser is present tense.

The infinitive is at læse = to read.

So:

• jeg læser = I read / I am reading
• deltageren læser = the participant reads / is reading

Like English, the Danish present tense can sometimes translate either as a simple present or a present progressive, depending on context.

Because Danish verbs do not conjugate for person the way English verbs do.

In English, we say:

• I read
• you read
• he/she reads

But in Danish, the present-tense verb form stays the same:

• jeg læser
• du læser
• han læser
• deltageren læser

That makes Danish verb conjugation simpler than English in this area.

A rough guide is something like LEH-ser, but the Danish æ sound is important.

• læ- has a vowel somewhat like the e in bed, but not exactly the same
• -ser is usually pronounced softly, not with a strong English r

So læser is approximately LEH-suh / LEH-ser, depending on accent and how detailed you want to be. The real Danish pronunciation is smoother than an English spelling can show.

A rough pronunciation guide is something like DEL-ta-geh-ren, though the real Danish sounds are softer and more reduced than that.

A few useful points:

• del sounds somewhat like English del
• ta is a light syllable
• ger is not pronounced like hard English ger in tiger
• the final -en is often light and unstressed

The exact pronunciation depends a little on accent, but the main challenge is learning the rhythm and reduced endings.

Yes, it is a normal and useful word. It means participant or sometimes attendee, depending on context.

For example:

• en deltager i kurset = a participant in the course
• mange deltagere = many participants

It is a good practical vocabulary word, especially in formal, educational, or event-related contexts.

Yes. Danish present tense often covers both ideas:

• The participant reads the book
• The participant is reading the book

Context tells you which meaning is intended. If this is just a standalone exercise sentence, either interpretation may be acceptable depending on the translation style being used.

Because the sentence is definite, not indefinite.

It says:

• deltageren = the participant
• bogen = the book

If you wanted a participant reads a book, you would use the indefinite articles:

• en deltager læser en bog

So the sentence is specific, not general.

Yes, but usually when there is an adjective.

Without an adjective, Danish typically uses the suffixed definite form:

• bogen = the book

With an adjective, Danish usually uses both a separate definite marker and a definite-style noun phrase:

• den interessante bog = the interesting book

So in your sentence, there is no adjective, which is why the simple suffixed forms deltageren and bogen are used.

It would be:

En deltager læser en bog.

That means:

A participant reads a book.

Comparison:

• Deltageren læser bogen. = The participant reads the book.
• En deltager læser en bog. = A participant reads a book.

This is a very useful contrast for learning Danish noun forms.