Learn Hardcore Portuguese (Portugal): Para sobreviver no inverno, eu visto um casaco grosso. - To survive in winter, I wear a thick coat.

In Portuguese, when you express purpose (in order to survive), you normally use para + infinitive.
So para sobreviver = in order to survive / to survive.

If you drop para and say Sobreviver no inverno, eu visto…, it sounds wrong and unfinished to a native speaker. You must keep para (or a synonym like a fim de) to show that this is a purpose clause.

What exactly does no mean in no inverno?

No is a contraction of em + o (in + the).

em = in
o = the (masculine singular)
em + o → no

So no inverno literally means in the winter. You cannot say em o inverno; you must contract to no.

Why is inverno not capitalised, while in English we often write Winter with a capital letter?

In Portuguese, names of the seasons (primavera, verão, outono, inverno) are written with a lowercase letter, even in more formal writing.
So no inverno is the standard spelling; no Inverno would only appear in very special stylistic or poetic contexts, not in normal usage.

Could I say para sobreviver ao inverno instead of para sobreviver no inverno? Is there a difference?

Yes, para sobreviver ao inverno is also correct, and it literally means to survive the winter.

sobreviver ao inverno (a + o → ao) focuses on surviving the whole winter as something you have to get through.
sobreviver no inverno (em + o → no) focuses more on surviving during the winter, in that season or those conditions.

The difference is subtle; both are natural in European Portuguese.

Is the pronoun eu necessary here? Can I say Para sobreviver no inverno, visto um casaco grosso?

You can absolutely drop eu:
Para sobreviver no inverno, visto um casaco grosso.

Portuguese is a “null-subject” language, so the verb ending -o in visto already tells us the subject is eu. You usually include eu only for emphasis or contrast (e.g. Eu visto um casaco grosso, tu não).

Why is the verb visto and not something like uso or ponho? What’s the difference?

vestir (here visto) = to put clothes on / to dress in.
- Eu visto um casaco grosso. → I put on / wear a thick coat.
usar = to wear (in general), to use.
- No inverno, uso um casaco grosso. → In winter, I (usually) wear a thick coat.
pôr (here ponho) = to put (on).
- No inverno, ponho um casaco grosso. → In winter, I put on a thick coat.

In this sentence, visto focuses slightly more on the act of dressing, but in practice all three verbs can appear in similar contexts, with small nuance differences.

What’s the difference between vestir and vestir-se? Could I say eu visto-me um casaco grosso?

vestir is transitive: it takes a direct object (the clothes).
- Eu visto um casaco grosso.
vestir-se is reflexive: to get dressed (in general).
- Eu visto-me. = I get dressed.
- Eu visto-me com um casaco grosso. is possible but less common/natural here.

Eu visto-me um casaco grosso is not idiomatic; you either say Eu visto um casaco grosso or Eu visto-me (without the object).

Why does grosso come after casaco? In English, the adjective comes before the noun (“thick coat”).

In Portuguese, the default order is noun + adjective:
um casaco grosso (coat thick).

Adjective + noun does exist, but it is more marked, poetic, or can change the nuance/meaning. Um grosso casaco would sound unusual or literary. For normal speech, stick to um casaco grosso.

Does grosso mean “thick” or “heavy”? Could I use quente instead?

Grosso literally means thick (physically bulky, with a lot of material). It implies warmth indirectly because thick clothes usually keep you warm.

um casaco grosso = a thick (and therefore warm) coat
um casaco quente = a warm coat (focuses directly on the warmth)

Both are fine:
Para sobreviver no inverno, eu visto um casaco quente. is also natural.

Do I really need the comma after inverno?

When a subordinate clause comes first (Para sobreviver no inverno), standard punctuation in Portuguese uses a comma before the main clause:

Para sobreviver no inverno, eu visto um casaco grosso.

If you invert the order, you normally don’t use a comma:

Eu visto um casaco grosso para sobreviver no inverno.

So with the current word order, the comma is recommended.

Is visto here related to ver (“to see”)? It looks like “seen”.

The form visto exists in two different verbs:

vestir → eu visto (I dress / I put on) – present tense, 1st person singular.
ver → visto (seen) – past participle, as in tenho visto (I have seen).

In this sentence, the context and the object um casaco grosso make it 100% clear that visto is from vestir, not from ver.

How do you pronounce this sentence in European Portuguese?

Very approximately in English-like syllables (European Portuguese):

Para sobreviver no inverno, eu visto um casaco grosso.
- PAH-ruh suh-breh-vee-VAIR noo een-VAIR-noo, ew VEESH-too oong kuh-ZAH-koo GROH-soo.

Key points:

Final -o in inverno, casaco, grosso is pronounced like a short -oo sound.
The s in visto is pronounced like sh: VEESH-too.
eu sounds like English “ehw” (ew).

Would this sentence be different in Brazilian Portuguese?

Grammatically, it’s fine in Brazilian Portuguese too:

Para sobreviver no inverno, eu visto um casaco grosso.

Differences:

Pronunciation is different (Brazilian visto has an s sound, not sh).
Brazilians might more often say um casaco bem grosso or prefer uso:
- No inverno, eu uso um casaco bem grosso.