Jeg forstår ikke delen om grammatik i teksten.

Because forstår is the present tense form of the verb at forstå (to understand).

In Danish, the present tense is often made by adding -r to the infinitive:

• at forstå = to understand
• forstår = understand / am understanding

So Jeg forstår ikke ... means I do not understand ...

In a normal Danish main clause, ikke usually comes after the finite verb.

So the pattern here is:

• Jeg = subject
• forstår = verb
• ikke = negation

That gives:

• Jeg forstår ikke ... = I do not understand ...

This is different from English, where we use do not understand. Danish does not need an extra do here.

Because delen is the definite form, meaning the part.

In Danish, the definite article is often added to the end of the noun instead of appearing as a separate word in front.

So:

• en del = a part
• delen = the part

That is why you see delen instead of a separate word for the.

Danish usually puts definiteness on the noun itself.

Examples:

• en tekst = a text
• teksten = the text
• en del = a part
• delen = the part

So English uses a separate article:

• the part
• the text

But Danish often uses an ending:

• delen
• teksten

Here om means about.

So:

• delen om grammatik = the part about grammar

This is a very common use of om when talking about a topic:

• en bog om historie = a book about history
• en artikel om sprog = an article about language

Because grammatik here is being used in a general sense: grammar as a subject or topic.

So:

• delen om grammatik = the part about grammar

If you said grammatikken, that would mean the grammar, which sounds more specific. In this sentence, Danish naturally uses the bare noun because it is talking about the topic in general.

Most naturally, i teksten goes with delen om grammatik.

So the structure is:

• Jeg forstår ikke = I do not understand
• delen om grammatik i teksten = the part about grammar in the text

In other words, it means the speaker does not understand the grammar-related part that is found in the text.

Because Danish normally uses i for something that is inside a text or part of its content.

So:

• i teksten = in the text

Using på would usually not be the normal choice here. English sometimes says in the text, and Danish matches that with i teksten.

The sentence follows a very common Danish main-clause pattern:

• Jeg = subject
• forstår = finite verb
• ikke = negation
• delen om grammatik i teksten = object / noun phrase

So the overall order is:

Subject + Verb + Negation + Object

That makes this sentence very typical and useful as a model:

• Jeg kender ikke bogen. = I do not know the book.
• Jeg kan ikke finde svaret. = I cannot find the answer.

Yes, but the meaning or style can shift a little.

• delen = the part
• den del = that part / the part

In many cases, delen is the most straightforward form. Den del is often used when you want extra emphasis, contrast, or when there is more structure around the noun.

For example:

• Jeg forstår ikke den del om grammatik. can sound a bit more pointed, like that part about grammar

But in your sentence, delen is perfectly natural.

This is a useful question because Danish word order changes in subordinate clauses.

In a main clause:

• Jeg forstår ikke delen om grammatik i teksten.

In a subordinate clause, ikke usually comes before the finite verb:

• ..., fordi jeg ikke forstår delen om grammatik i teksten.
• ..., som jeg ikke forstår.

So the difference is:

Main clause:

• jeg forstår ikke

Subordinate clause:

• jeg ikke forstår

This is one of the most important word-order differences in Danish grammar.