Jeg går først ud, når det holder op med at regne.

In Danish, the present tense is often used for future meaning when the time is clear from the context.

So Jeg går først ud, når det holder op med at regne uses present tense, but it means something like I’ll only go out when it stops raining.

This is very normal in Danish. English can sometimes do this too, especially in time clauses:

• I’ll go out when it stops raining
• not usually when it will stop raining

So Danish is following a similar pattern here.

Here, først means only then / not until then, not just first in the sense of before everyone else.

In this sentence, Jeg går først ud means:

• I won’t go out until later
• I’ll only go out then

So the idea is not I go out first, but rather I go out only when the condition is met.

That is a very common use of først in Danish.

Because gå ud is the natural expression for go out.

• gå = go / walk
• ud = out

Together, gå ud means go outside / go out.

A lot of Danish verbs work like this, with a verb plus a small particle such as ud, op, ned, ind, and so on.

So:

• jeg går = I go / I walk
• jeg går ud = I go out

Når means when, and it is used when the speaker sees the event as expected or as something that will happen.

Hvis means if, and it is used for conditions that are more uncertain.

So in this sentence:

• når det holder op med at regne = when it stops raining

This suggests the speaker expects the rain to stop at some point.

If you said:

• hvis det holder op med at regne

that would sound more like if it stops raining, with more uncertainty.

Here, det is a dummy subject, like it in English weather expressions.

English says:

• it is raining
• it stops raining

Danish does the same:

• det regner
• det holder op med at regne

So det does not refer to a specific thing. It is just the grammatical subject required by the sentence.

This is a very common Danish structure:

• holde op med at + infinitive

It means stop + -ing in English.

So:

• holde op med at regne = stop raining
• literally: stop with to rain

Other examples:

• Hun holder op med at tale. = She stops talking.
• Vi holdt op med at vente. = We stopped waiting.

So in your sentence, det holder op med at regne means it stops raining.

Jeg går først ud is the more natural word order here because først is closely tied to the idea of when I go out.

Putting først before ud makes the timing feel central:

• Jeg går først ud = I only go out then / I won’t go out until then

If you say Jeg går ud først, it can sound more like I go out first in contrast to doing something else afterward, depending on context.

So the position of først matters for nuance.

Yes. You could also say:

• Når det holder op med at regne, går jeg først ud.

That is also correct.

But then the main clause has inversion:

• går jeg
• not jeg går

This is because Danish has V2 word order in main clauses. When something else comes first, the finite verb comes before the subject.

So:

• Jeg går først ud, når det holder op med at regne.
• Når det holder op med at regne, går jeg først ud.

Both are grammatical.

Because når det holder op med at regne is a subordinate clause.

In Danish, subordinate clauses usually keep the subject before the verb:

• det holder
• not holder det

Inversion happens in main clauses after something is placed first, but not in ordinary subordinate clauses.

So:

• Når det holder op med at regne, går jeg først ud.
  
  • subordinate clause: det holder
  • main clause: går jeg

That difference is important in Danish word order.

Yes, you could say:

• Jeg går først ud, når det ikke regner mere.

That means almost the same thing: I’ll only go out when it’s not raining anymore.

The difference is mostly one of phrasing:

• når det holder op med at regne = when it stops raining
• når det ikke regner mere = when it isn’t raining anymore

Both are natural. The first one focuses on the stopping event; the second focuses on the resulting situation.

Yes. Regne is the infinitive.

That is because it comes after at in the structure holde op med at + infinitive.

So:

• at regne = to rain

Compare:

• Det regner. = It is raining.
  Here regner is a finite present-tense verb.
• Det holder op med at regne. = It stops raining.
  Here regne is an infinitive.

A very literal breakdown is:

• Jeg = I
• går = go
• først = only then / not until then
• ud = out
• når = when
• det = it
• holder op med at regne = stops raining

So a fairly literal version would be:

• I go only out when it stops raining

But the natural English meaning is:

• I’ll only go out when it stops raining
• or I won’t go out until it stops raining