Learn Hardcore Portuguese (Brazil): Hoje estou ocupado, não posso caminhar na cidade. - Today I am busy, I cannot walk in the city.

estar ocupado = to be busy right now, temporarily
- Hoje estou ocupado = I am busy today (but not always).
ser ocupado would mean being a busy person by nature/characteristic, which is unusual and sounds odd here.
You would only use sou ocupado in a very specific context like:
- Eu sou muito ocupado, quase nunca tenho tempo.
  I’m (generally) a very busy person; I almost never have time.

In your sentence, being busy is a temporary state today, so estou ocupado is correct.

Why can the subject eu be left out? Why don’t we say Hoje eu estou ocupado?

In Portuguese, the verb ending shows who the subject is, so the subject pronoun is often omitted:

estou = I am
estás / está = you are
estamos = we are

So (Eu) estou ocupado is understood as I am busy even without eu.

You can say Hoje eu estou ocupado, and it’s correct. Adding eu:

can add emphasis: I am busy (as opposed to someone else).
is more common in spoken Portuguese when you want to be very clear or expressive.

Both are grammatically fine:

Hoje estou ocupado.
Hoje eu estou ocupado.

Can I say Estou ocupado hoje instead of Hoje estou ocupado? Is there a difference?

Yes, you can say both:

Hoje estou ocupado.
Estou ocupado hoje.

They both mean the same thing: I’m busy today.

Subtle tendency:

Hoje estou ocupado slightly highlights today at the beginning.
Estou ocupado hoje is a very neutral, natural order.

In everyday speech, both are completely normal.

If I’m a woman, do I say ocupado or ocupada?

Adjectives in Portuguese agree with the gender of the person:

Male speaker: Hoje estou ocupado.
Female speaker: Hoje estou ocupada.

Same with plurals:

Group of only men or mixed group: Estamos ocupados.
Group of only women: Estamos ocupadas.

How do you pronounce hoje and cidade? They don’t sound like English.

Hoje

Roughly like: “OH-zhee” (Brazilian accent)
h is silent.
j sounds like the s in measure or vision.

Cidade

Roughly like: “see-DAH-jee” (Brazilian)
Final -de in Brazil often sounds like -jee.
Stress is on the DA: ci-DA-de.

So the whole sentence in a typical Brazilian pronunciation is something like:

“OH-zhee es-TOH oo-koh-PAH-doo, nao POH-soo kah-mee-NYAR na see-DAH-jee.”

Why is it não posso caminhar and not something like não posso de caminhar or não posso para caminhar?

When poder (can / to be able to) is followed by another verb, you use the bare infinitive of the second verb, with no preposition:

posso caminhar = I can walk
não posso caminhar = I can’t walk

So:

❌ não posso de caminhar
❌ não posso para caminhar

are incorrect here.

This pattern is the same with many modal-like verbs:

quero caminhar (I want to walk)
preciso caminhar (I need to walk)
vou caminhar (I’m going to walk)

What’s the difference between caminhar and andar? Could I say não posso andar na cidade?

Both can relate to walking, but their usage differs.

caminhar

Focuses on the act of walking, often as an activity or exercise.
Gosto de caminhar de manhã. – I like to go for a walk in the morning.

andar

More general: to walk, to go, to move, to ride (depending on context).
Ele anda muito rápido. – He walks very fast.
Ando de ônibus. – I ride/go by bus.

In your sentence, you can say:

Hoje estou ocupado, não posso caminhar na cidade.
Hoje estou ocupado, não posso andar na cidade.

Both are understandable.
Caminhar na cidade suggests “go for a walk in the city.”
Andar na cidade can sound a bit more general: “walk/move around in the city.” Context decides which feels more natural.

What exactly is na in na cidade? Why not just em cidade or em a cidade?

Na is a contraction of:

em (in / on / at) + a (the, feminine singular)
→ em + a = na

So:

na cidade = in the city

You do not say:

❌ em a cidade (you must contract it)
❌ em cidade (this would mean “in a city / in city” but sounds unnatural here; usually you need the article).

Other examples:

no trabalho = em + o trabalho (at work)
nos Estados Unidos = em + os Estados Unidos (in the United States)
nas casas = em + as casas (in the houses)

Could I say pela cidade instead of na cidade? What’s the difference?

Yes, but it changes the nuance:

caminhar na cidade = walk in the city (location)
caminhar pela cidade = walk around/through the city (movement through different parts)

pela is usually:

por + a → pela
and often implies movement, route, or passing through.

So:

Hoje estou ocupado, não posso caminhar pela cidade.
= I’m busy today, I can’t walk around the city.

Why is the negative não before posso and not after, like posso não?

In standard Portuguese, não goes before the verb it negates:

não posso = I cannot
não quero = I do not want
não entendo = I do not understand

So:

não posso caminhar = I cannot walk.

Posso não… is possible in some contexts but has a different meaning, closer to:

I may not … / I might not … (more about possibility, not simple inability).

Example:

Posso não conseguir chegar a tempo.
I might not manage to arrive on time.

In your sentence you mean I can’t (I’m not able to), so não posso caminhar is the correct structure.

Why is it posso and not consigo? What’s the difference between não posso and não consigo?

Both can translate as can’t, but they’re used differently:

poder (posso, não posso)

relates to permission, possibility, external conditions.
Hoje estou ocupado, não posso caminhar na cidade.
→ I can’t (I’m not able / my circumstances don’t allow it).

conseguir (consigo, não consigo)

relates to managing to do something, succeeding in doing it, often ability or difficulty.
Estou cansado, não consigo caminhar muito.
→ I can’t (I’m not able physically / I don’t manage to).

In your sentence:

não posso caminhar = I can’t because I’m busy today (schedule, situation).
If you said:
não consigo caminhar here, it would suggest I’m physically unable or having difficulty walking.

Why isn’t it Estou caminhando na cidade for “I’m walking in the city”? What’s the role of caminhar here?

In your sentence, caminhar appears as an infinitive after posso:

não posso caminhar = I can’t walk.

If you wanted to say I’m walking in the city (right now), you would use the present progressive:

Estou caminhando na cidade. – I am walking in the city.

In the original sentence, the idea is I can’t go for a walk in the city today, not that you’re currently walking. So:

estou ocupado (I am busy) – simple present of estar
não posso caminhar (I cannot walk) – poder
- infinitive caminhar

Is this sentence formal or informal? Can I use it in any context?

The sentence is neutral and polite. It’s suitable in almost any context:

Talking to a friend: totally fine.
Talking to a colleague or boss: also fine.
Sending a message or email: fine.

If you wanted it a bit more formal/polite, you might expand it:

Hoje estou ocupado, infelizmente não posso caminhar na cidade com você.
Today I’m busy, unfortunately I can’t walk in the city with you.

But as it is, the sentence is already acceptable in both informal and semi‑formal situations.