Min datter samler pant på terrassen, når gæsterne har været her.

Because in Danish, a possessive like min, din, hans, vores, etc. normally takes a noun in the indefinite form.

So you say:

• min datter = my daughter
• min bil = my car
• vores hus = our house

Not:

• min datteren
• min bilen

This is different from English, where the noun form does not change.

Pant usually means deposit-return containers such as bottles and cans that can be returned for money.

So samler pant means something like:

• collecting empty bottles and cans for deposit refund

It is a very common everyday word in Denmark because many drink containers have a refund value.

Because pant is often treated like an uncountable or collective noun in this context.

So Danish commonly says:

• samle pant = collect deposit bottles/cans
• aflevere pant = return deposit containers

You do not usually need et or en here.

The present tense in Danish is often used for habitual or general repeated actions, just like in English.

So Min datter samler pant ... means that this is something she typically does, not necessarily something happening right this second.

Compare:

• Hun samler pant, når gæsterne har været her.
  = She collects the bottles/cans when the guests have been here.

This describes a repeated pattern.

Når is used for something that happens whenever or when it is expected to happen.

Hvis is used more for if in the sense of a condition or possibility.

Here, the sentence describes a normal repeated situation:

• når gæsterne har været her = when/whenever the guests have been here

That suggests this is what usually happens after guests visit.

If you used hvis, it would sound more like:

• if the guests have been here

which is less natural for a regular routine.

Because har været her is the present perfect, and it shows that the guests’ visit is completed before the daughter collects the deposit bottles/cans.

So the timeline is:

1. the guests are here
2. the guests have been here / have visited
3. then the daughter collects the empties

In Danish, this is very natural after når when you want to show one action is already completed before the next one happens.

• når gæsterne har været her
  = when the guests have been here / after the guests have been here

Using var her would sound more like a simple past statement and would not fit this habitual structure as well.

Gæsterne means the guests. The ending -ne is the definite plural ending.

So:

• en gæst = a guest
• gæster = guests
• gæsterne = the guests

Danish often adds definiteness as an ending on the noun.

Because terrassen means the terrace/patio. The -en ending marks the noun as definite.

So:

• en terrasse = a terrace / patio
• terrassen = the terrace / patio

In this sentence, it is a specific terrace, presumably the one at the home being talked about.

Literally, it means on the terrace, but in natural English it may often be better understood as:

• out on the terrace
• on the patio
• outside on the terrace

Danish på is used for a lot of locations where English may choose on, in, or at depending on context.

Her means here.

In gæsterne har været her, it means the guests have been here at this place, usually the speaker’s or subject’s home.

So it is not just a random here. It refers to the location being discussed.

Because når gæsterne har været her is a subordinate clause, and subordinate clauses in Danish normally keep the subject before the verb.

So:

• når gæsterne har været her
  = when the guests have been here

This is normal subordinate-clause order.

By contrast, har gæsterne været her? would be a question:

• Have the guests been here?

So the sentence uses normal statement word order inside the når clause.

Because når gæsterne har været her is a subordinate clause, and Danish writing commonly places a comma before subordinate clauses.

So the comma helps separate:

• Min datter samler pant på terrassen
  from
• når gæsterne har været her

This is a punctuation feature of standard written Danish.

Yes. You could say:

• Når gæsterne har været her, samler min datter pant på terrassen.

That is also correct.

When the subordinate clause comes first, the main clause follows normal Danish V2 word order, so you get:

• ..., samler min datter ...

not:

• ..., min datter samler ...

This is a very important Danish word-order pattern.

Yes, very much so. It sounds natural and everyday.

In Denmark, because bottle and can deposits are common, people often talk about:

• samle pant = collect deposit bottles/cans
• aflevere pant = return them for refund

So this phrase is normal, practical Danish, not unusual or literary language.