In Portuguese specifically, yes-or-no questions look the same as declarative sentences, that is, the word order is kept unchanged. A few examples: 

Declarative
Tu estás no Porto. 
You are in Porto.

Interrogative
Tu estás no Porto?
Are you in Porto?

As you see, contrary to other languages such as English, the verb follows the subject in both declarative and interrogative sentences.

Because interrogative and declarative sentences look the same, it is important to intonate interrogative sentences properly so that they come across as intended. 

For instance, when asking, Tu estás no Porto?  you want to finish off in a rising tone so that it clearly sounds like a question. Read on.

Companion read

Related

Articles

Lessons

Blanks

E porque não?

Fill in the blanks with the question words.

Fill in the blanks

Onde moras?

Fill in the blanks with the missing question words and prepositions.

Fill in the blanks

As is the case for open-ended questions, yes-or-no questions do perfectly well without any auxiliary verb (which is not the case in English): 

O carro tem gasolina suficiente?
Does the car have enough gas? 

Ele já chegou de Inglaterra?
Did he arrive from England already?

Further reading! Read the following article to learn more about Portuguese verb usage compared to English: Portuguese Verb Usage and Tenses: A Practical Guide Anchored to English.

How to answer a yes-or-no question

Usually, we don’t answer these questions with a bare “yes” or “no”. Instead, we repeat the verb used in the question: 

– Estás na Suécia?
– Sim, estou. / Não, não estou. 
– Are you in Sweden?
– Yes, I am. / No, I am not.

– Já viste este filme? 
– Sim, já vi. / Não, ainda não vi.
– Have you already seen this movie?
– Yes, I have. / No, I haven’t.

Affirmative sentences

Like in English, we also utter those reassuring “add-ons” at the end of sentences. Let’s look at a few affirmative cases:

Ele gosta de ir ao cinema, não gosta?
He likes going to the cinema, doesn’t he?

Tu dormes muito, não dormes?
You sleep a lot, don’t you?

As you can see, we form question tags for affirmative sentences by putting together the negative não and the verb from the main sentence.

Alternatively, you can use the universal question tag: não é? With the latter, you won’t even need to mind the verb in the main sentence: 

Ele gosta de cinema, não é?
He likes cinema, doesn’t he?

Tu dormes muito, não é?
You sleep a lot, don’t you?

Negative sentences

Let’s now look at how it works with negative sentences:

Ele não gosta de pintar, pois não?
He doesn’t enjoy painting, does he?

Tu não fumas muito, pois não?
You don’t smoke that much, do you?

As you can see above, concerning negative sentences, the question tag always looks the same – pois não? – regardless of the verb in the main sentence.

If you want to learn more about asking questions in Portuguese and many other basic topics, consider All-round Beginners A1 – a modular course that gives a solid foundation to build on.