Não importa se chover, eu quero caminhar na cidade.

Because after se meaning if, Portuguese often uses the future subjunctive when talking about a possible future situation.

So in:

Não importa se chover...

chover = future subjunctive of chover.

This is very common in Portuguese:

• Se chover, fico em casa. = If it rains, I stay home.
• Se eu tiver tempo, eu vou. = If I have time, I’ll go.
• Se ele vier, avise-me. = If he comes, let me know.

A useful thing to know: for some verbs, the future subjunctive looks exactly like the infinitive. That is why chover looks unchanged.

Also, chover is an impersonal weather verb, so you do not use a subject like it the way English does.

Here, se means if.

The sentence is expressing a condition:

• Não importa se chover = It doesn’t matter if it rains

Portuguese se can also mean whether, depending on context:

• Não sei se ele vem. = I don’t know whether he is coming.

So the word is the same, but the meaning depends on the sentence.

Não importa means it doesn’t matter.

This is an impersonal expression in Portuguese. English uses a dummy subject, it, but Portuguese usually just says the verb in the 3rd person singular:

• Não importa. = It doesn’t matter.
• Importa muito. = It matters a lot.

So in your sentence:

• Não importa se chover = It doesn’t matter if it rains

You do not need a separate word for it.

Portuguese often avoids the kind of dummy subject that English uses.

In English, you say:

• It doesn’t matter
• It is raining

In Portuguese, those are usually just:

• Não importa
• Está chovendo or Chove

That is because Portuguese does not need a meaningless subject like English it in these cases.

Weather verbs such as chover, nevar, and trovejar are normally used without a real subject.

Yes, it could be omitted.

Portuguese often leaves out subject pronouns when the verb ending already shows who the subject is:

• Quero caminhar na cidade. = I want to walk in the city.

Including eu adds a little emphasis, contrast, or clarity:

• Eu quero caminhar na cidade. = I want to walk in the city.

So both are correct. In everyday Brazilian Portuguese, dropping eu is very common unless you want emphasis.

The comma separates the subordinate clause from the main clause.

Structure:

• Não importa se chover = subordinate idea
• eu quero caminhar na cidade = main idea

In Portuguese, when an introductory clause comes before the main clause, a comma is often used:

• Se chover, eu fico em casa.
• Quando ele chegar, eu saio.

So the comma here is natural and helps readability.

Both can relate to walking, but they are not always identical.

Caminhar

Usually means to walk in a more direct sense, often more deliberate or physical.

• Gosto de caminhar de manhã. = I like to walk in the morning.

Andar

Can mean to walk, but also more broadly to move around, to go around, or even to function/go by in other contexts.

• Andar pela cidade = to walk/go around the city
• O relógio não anda. = The clock doesn’t work/run

In your sentence, caminhar is fine and clear if the idea is literally walking.

Good question. Both are possible, but they give slightly different feelings.

na cidade

Means in the city. It emphasizes location: the walking happens within the city.

• Quero caminhar na cidade. = I want to walk in the city.

pela cidade

Means through / around the city. It sounds more like moving around different parts of the city.

• Quero caminhar pela cidade. = I want to walk around the city.

So na cidade is not wrong, but pela cidade may sound more natural if the idea is wandering or strolling around.

Yes, it is understandable and basically correct, but many Brazilians might phrase it a little differently depending on the exact meaning.

Possible alternatives:

• Mesmo se chover, quero caminhar pela cidade.
  = Even if it rains, I want to walk around the city.

• Não importa se chover, quero caminhar pela cidade.
  = It doesn’t matter if it rains, I want to walk around the city.

• Ainda que chova, quero caminhar pela cidade.
  = Even if it rains, I want to walk around the city.
  (more formal/literary)

So your sentence works, but pela cidade may sound a bit more natural than na cidade if the idea is walking around town.

Yes, you could, but it changes the structure slightly.

Não importa se chover

= It doesn’t matter if it rains
This is more impersonal.

Não me importo se chover

= I don’t mind if it rains
This is personal: it focuses on my attitude.

So both are good, but they are not exactly the same in tone:

• Não importa... = more neutral / impersonal
• Não me importo... = more personal

Normally, yes, when it means literal rain.

Portuguese treats weather verbs as impersonal:

• Vai chover. = It’s going to rain.
• Se chover, eu não saio. = If it rains, I’m not going out.

There is no subject like English it.

However, in figurative language, a subject can appear:

• Choveram críticas. = Criticism rained down.
• Choveram mensagens no meu celular. = Messages poured into my phone.

But in normal weather meaning, chover is typically impersonal.