Min veninde sælger sin gamle lampe, mens hun beholder reolen fra stuen.

Veninde means female friend. Danish often makes this distinction:

• ven = friend, often male or unspecified
• veninde = female friend

So Min veninde means my female friend.

Because the speaker is specifically referring to a female friend. Danish uses veninde when the person is a woman or girl.

So:

• min ven = my friend / my male friend
• min veninde = my female friend

This is one of the most important Danish points in the sentence.

Danish uses sin/sit/sine when the possessor is the subject of the clause. Here, the subject is Min veninde, and the lamp belongs to her, so Danish uses sin.

• Min veninde sælger sin gamle lampe = My friend sells her own old lamp.

If you used hendes, it would usually suggest that the lamp belongs to some other woman, not the subject.

Compare:

• Hun sælger sin lampe = She sells her own lamp.
• Hun sælger hendes lampe = She sells another woman’s lamp.

Because sin/sit/sine must agree with the noun they describe.

Here the noun is lampe, which is a common gender singular noun, so you use sin.

The pattern is:

• sin
  • common gender singular noun
• sit
  • neuter singular noun
• sine
  • plural noun

Examples:

• sin lampe
• sit hus
• sine bøger

Because after a possessive like sin, adjectives usually take the -e form.

So:

• en gammel lampe = an old lamp
• sin gamle lampe = her own old lamp

This is very common in Danish:

• min nye bil
• hendes store hus
• vores gamle bøger

So the -e form here is expected.

Because Danish does not normally use an article when a possessive comes first.

In English we say her old lamp, not the her old lamp, and Danish works similarly:

• sin gamle lampe = her old lamp
• not den sin gamle lampe

Possessives already make the noun specific, so no separate article is needed.

Reolen is the definite form of reol.

• reol = a shelf / a bookcase / a shelving unit
• reolen = the shelf / the bookcase

Danish often adds definiteness as an ending:

• en bil → bilen
• en stol → stolen
• en reol → reolen

So reolen fra stuen means the bookcase from the living room.

Reol usually means a bookcase, shelving unit, or set of shelves. The exact English translation depends on context.

In this sentence, reolen fra stuen probably means something like:

• the bookcase from the living room
• the shelving unit from the living room

Literally, fra stuen means from the living room.

It describes which reol we are talking about: the one that comes from or belongs in the living room.

So:

• reolen fra stuen = the bookcase/shelving unit from the living room

This is a common Danish way to identify something:

• bordet fra køkkenet = the table from the kitchen
• lampen fra gangen = the lamp from the hallway

Because stuen is the definite form: the living room.

• en stue = a living room
• stuen = the living room

So fra stuen means from the living room, not from a living room.

Mens means while.

It connects two actions happening at the same time, or two contrasting actions:

• Min veninde sælger sin gamle lampe, mens hun beholder reolen fra stuen.
• My friend sells her old lamp, while she keeps the bookcase from the living room.

So one thing is being sold, while another thing is being kept.

Because mens introduces a subordinate clause, and Danish word order changes in subordinate clauses.

In a main clause, Danish usually follows the verb-second pattern:

• Hun beholder reolen.

But after a subordinating conjunction like mens, the subject usually comes before the finite verb:

• mens hun beholder reolen

This is normal subordinate-clause order in Danish.

They are both in the present tense.

• sælger = sells / is selling
• beholder = keeps / is keeping

In Danish, the present tense can often cover both simple present and present progressive, depending on context.

So this sentence could mean:

• My friend sells her old lamp while she keeps the bookcase from the living room or more naturally in English,
• My friend is selling her old lamp while keeping the bookcase from the living room

Not necessarily. The Danish present tense can describe:

• something happening now
• a general situation
• a near-future arrangement in some contexts

Here it most naturally sounds like a current situation or plan: she is selling one item and keeping another.

Because mens hun beholder reolen fra stuen is a subordinate clause, and Danish often uses a comma before such clauses.

You may see some variation in comma style in Danish, but a comma here is completely normal and common.

No, not normally. Sin points back to the subject of the clause.

So in this sentence, sin gamle lampe refers back to Min veninde. It means the lamp belongs to the friend.

If the lamp belonged to another woman, Danish would usually use hendes instead.

Not perfectly. A very close literal version would be:

• My female friend sells her own old lamp, while she keeps the bookcase from the living room.

But more natural English might be:

• My friend is selling her old lamp while keeping the bookcase from the living room.

So the grammar matches closely in some places, but natural English may phrase it a little differently.