Jeg skal til at gå ud af huset, men så ser jeg, at det regner.

Skal often adds the idea of something that is about to happen, is planned, or is expected to happen.

• Jeg går ud af huset = I go / I’m going out of the house
• Jeg skal gå ud af huset = I’m going to go out of the house / I have to go out of the house

In this sentence, jeg skal til at gå ud af huset makes it even more specific: the speaker is just about to leave.

Skal til at means something like be about to, be just going to, or be on the point of doing something.

So:

• Jeg skal til at gå = I’m about to leave / I’m just going to leave

This is a very common Danish way to talk about an action that is about to begin.

This is a fixed Danish structure:

• skal = modal verb
• til at = part of the expression meaning about to
• gå = the main verb in infinitive form

So skal til at gå works as one unit meaning am about to go.

You should not try to translate each word too literally. The whole phrase is what matters.

Gå ud means go out.
Gå ud af huset is more specific: go out of the house.

• gå ud = go out
• gå ud af huset = go out of the house / leave the house

Danish often uses these directional combinations very naturally, and ud af means out of.

Ud means out, and af often means of/from in this kind of expression. Together, ud af means out of.

Examples:

• ud af bilen = out of the car
• ud af døren = out of the door
• ud af huset = out of the house

So this is a normal prepositional combination, not something unusual.

Huset is the definite form, meaning the house.

In Danish, definiteness is often shown by adding an ending to the noun:

• hus = house
• et hus = a house
• huset = the house

Here, ud af huset means out of the house.

Men means but.
Så here means something like then or at that point.

So men så ser jeg... means:

• but then I see...
• but then I notice...

It helps show the sequence of events: first the speaker is about to leave, then they notice that it is raining.

This is because Danish is a V2 language in main clauses. That means the finite verb usually comes in the second position.

In så ser jeg, så takes the first position, so the verb ser must come second, before the subject jeg.

Compare:

• Jeg ser det.
• Så ser jeg det.

This kind of inversion is very important in Danish main clauses.

Danish normally uses at to introduce a subordinate clause after verbs like see, know, think, and say.

So:

• jeg ser, at det regner = I see that it’s raining

The at here works like English that.

In everyday speech, some speakers may drop at in some contexts, but using it is standard and very common.

The det is a dummy subject, similar to English it in it’s raining.

Danish usually needs a subject in the clause, even when there is no real thing doing the action.

So:

• det regner = it is raining

The det does not refer to a specific object here. It is just required by the grammar.

Because Danish, like English, normally uses the present tense for something happening now.

• det regner = it is raining / it rains

In English, we usually say it is raining, but Danish simply uses the present tense form regner. Danish does not have a separate progressive form like English is raining.

Grammatically, it means see, but in natural English the idea is often closer to notice or realize.

• så ser jeg, at det regner = then I see that it’s raining
• more natural English: then I notice that it’s raining

In Danish, se is often used in places where English might prefer notice.

Yes. A few natural alternatives are:

• Jeg er på vej ud, men så ser jeg, at det regner.
  = I’m on my way out, but then I see that it’s raining.

• Jeg er lige ved at gå ud, men så ser jeg, at det regner.
  = I’m just about to go out, but then I see that it’s raining.

• Jeg skal lige til at gå, men så ser jeg, at det regner.
  = I’m just about to leave, but then I see that it’s raining.

The original sentence is perfectly natural, but Danish has several ways to express being about to do something.

A few things often matter for learners:

• jeg is often pronounced more like yai or ya depending on the speaker
• skal may sound a bit like sgal
• til at is often reduced in fast speech
• ud af may sound more connected than learners expect
• regner is pronounced roughly like rainer with Danish sounds, not like it looks to an English speaker

Also, in natural speech, Danish often links words together a lot, so the full sentence may sound smoother and less separated than it appears in writing.

Yes. Så is a very common word with several meanings depending on context.

It can mean:

• then
• so
• thus
• sometimes well in conversation

In this sentence, then is the best fit:

• men så ser jeg... = but then I see...

So you always need to interpret så from the situation, not just memorize one English translation.