Hun markerer de vigtigste ord på siden.

Hun means she.

You use hun as the subject pronoun for a female person:

• Hun læser. = She is reading.
• Hun markerer ... = She marks/highlights ...

The matching object form is usually hende = her:

• Jeg ser hende. = I see her.

Markerer is the present tense form of the verb at markere.

So:

• at markere = to mark / to highlight
• markerer = marks / is marking / highlights

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

• at læse → læser
• at skrive → skriver
• at markere → markerer

In this sentence, Hun markerer ... can mean either She marks ... or She is marking ..., depending on context.

Ord is a neuter noun, and it has the same form in both singular and plural in many contexts.

So:

• et ord = a word
• ord = words
• ordet = the word
• ordene = the words

In the sentence, de vigtigste ord means the most important words.

Here:

• de = the
• vigtigste = most important
• ord = words

So the whole noun phrase is plural.

De vigtigste means the most important.

It is the superlative form of vigtig = important.

The comparison forms are:

• vigtig = important
• vigtigere = more important
• vigtigst = most important

When the superlative comes before a noun with the, Danish usually uses:

• de vigtigste ord = the most important words

So vigtigste is the form used here because it is part of a definite phrase: the most important words.

Because Danish usually uses de before a plural noun phrase that is definite and includes an adjective.

Compare:

• vigtige ord = important words
• de vigtige ord = the important words
• de vigtigste ord = the most important words

So de works here as the definite article for the whole plural phrase.

På siden means on the page.

Breakdown:

• på = on
• siden = the page / the side, depending on context

In this sentence, because of ord and the general context of text, siden is best understood as the page.

So:

• Hun markerer de vigtigste ord på siden.
• She marks/highlights the most important words on the page.

Because siden is the definite form of side.

• en side = a page / a side
• siden = the page / the side

Danish often adds the definite article to the end of the noun:

• en bog → bogen = the book
• en side → siden = the page

So på siden literally means on the page.

No. Side can mean either side or page, depending on context.

Examples:

• på den anden side = on the other side
• på side 10 = on page 10
• på siden in a reading/writing context often means on the page

In this sentence, because she is marking words, page is the natural meaning.

The basic order is:

Subject + Verb + Object + Prepositional phrase

So:

• Hun = subject
• markerer = verb
• de vigtigste ord = object
• på siden = prepositional phrase

This is very normal Danish main-clause word order.

Yes.

Danish present tense often covers both:

• simple present: she marks
• present progressive: she is marking / highlighting

So Hun markerer de vigtigste ord på siden could naturally mean:

• She marks the most important words on the page
• She is highlighting the most important words on the page

The exact English translation depends on context.

Yes, in many contexts it is.

At markere can mean:

• to mark
• to highlight
• to indicate

If someone is working with text and selecting important words, English often prefers highlight. Danish can still use markere naturally in that situation.

So this sentence could be understood as:

• She marks the most important words on the page
• She highlights the most important words on the page

You usually put ikke after the finite verb in a main clause.

So:

• Hun markerer ikke de vigtigste ord på siden.
• She does not mark / is not marking the most important words on the page.

This is a useful pattern:

• Hun læser ikke. = She is not reading.
• Han skriver ikke. = He is not writing.

In a yes/no question, Danish usually puts the verb before the subject:

• Markerer hun de vigtigste ord på siden?
• Is she marking the most important words on the page? / Does she mark the most important words on the page?

So the word order changes from:

• Hun markerer ...
  to
• Markerer hun ...?

For a learner, the main thing is that vigtigste is the superlative form of vigtig.

Roughly:

• vigtig
• vigtigste = the same base word, plus a superlative ending

The spelling can look a bit heavy because of the consonant cluster, but learners should focus first on recognizing the pattern:

• vigtig → vigtigere → vigtigst / vigtigste

If you are speaking carefully, just aim for something close to VIG-ti-ste. Danish pronunciation is often less fully pronounced than the spelling suggests, so listening to native audio is especially helpful here.