Eu vou ao mercado antes de voltar para casa.

Ao is a contraction of a + o.

• a = to
• o = the (masculine singular article)

So ao mercado literally means to the market.

This kind of contraction is very common in Portuguese:

• a + o = ao
• a + a = à
• de + o = do
• em + o = no

So vou ao mercado is the normal contracted form of vou a o mercado, and the uncontracted version is not used.

Both can be correct, but they are not always used in exactly the same way.

In this sentence, ir a is a very standard way to say to go to a place:

• vou ao mercado = I go / I’m going to the market

You may also hear:

• vou para o mercado

In Brazilian Portuguese, ir para is also very common, especially in everyday speech. Very roughly:

• ir a can sound a bit more neutral or traditional
• ir para can emphasize destination a little more

In real Brazilian usage, both are common, and many speakers would also say:

• vou no mercado

That last one is very common in spoken Brazilian Portuguese, though some teachers and grammar books prefer vou ao mercado.

Because Portuguese normally uses antes de before a verb in the infinitive.

So:

• antes de voltar = before returning / before going back

This is a fixed pattern:

• antes de sair = before leaving
• antes de dormir = before sleeping
• antes de comer = before eating

You should think of antes de + infinitive as a common structure.

After antes de, Portuguese usually uses the infinitive.

So you get:

• antes de voltar para casa

not:

• antes de volto para casa

That would be incorrect.

Here, the subject of voltar is understood to be the same as the subject of the main verb: eu. So Portuguese does not need to repeat it.

In English, we often use a full clause:

• before I return home

But Portuguese often prefers:

• antes de voltar para casa

Yes, you can.

• antes de voltar para casa
• antes de eu voltar para casa

Both are possible.

The shorter version without eu is very natural when the subject is already clear. The version with eu makes the subject explicit and can sound a little more emphatic or a little more formal, depending on context.

Portuguese also allows this kind of structure with other subjects:

• antes de eles voltarem para casa = before they return home

So if you want to state the subject clearly, you can.

Because casa often appears without an article when it means home.

So:

• para casa = home / to home
• em casa = at home
• de casa = from home

This is very common and very important.

Compare:

• voltar para casa = to go back home
• voltar para a casa = to go back to the house

With a casa, you are usually talking about a specific house as a building. Without the article, casa often means home in a more general personal sense.

Because they behave differently.

Mercado normally takes an article:

• o mercado
• ao mercado

But casa, when it means home, often drops the article after certain prepositions:

• para casa
• em casa
• de casa

So the contrast is normal:

• ao mercado
• para casa

This is not random; it is just how these words are commonly used in Portuguese.

Yes. In most contexts, you can simply say:

• Vou ao mercado antes de voltar para casa.

Portuguese often leaves subject pronouns out when the verb already makes the subject clear. Since vou clearly means I go / I’m going, eu is optional.

You usually include eu when you want:

• emphasis
• contrast
• clarity

For example:

• Eu vou ao mercado, mas ele vai à farmácia.

Here eu helps create contrast with ele.

Vou is the present indicative of ir.

So grammatically, it is present tense. Depending on context, that present tense can be understood in different ways in English:

• I go to the market before going home
• I’m going to the market before going home
• I’ll go to the market before going home

One important point: this is not the future construction vou + infinitive.

For example:

• vou comprar pão = I’m going to buy bread

But in your sentence:

• vou ao mercado

Here vou keeps its basic meaning of go.

Yes. In Brazilian Portuguese, pra casa is extremely common in speech.

• para casa = standard full form
• pra casa = very common spoken contraction

So you will often hear:

• Eu vou ao mercado antes de voltar pra casa.

That is natural spoken Brazilian Portuguese. In careful writing or teaching materials, you will usually see para.

It can mean either, depending on context.

In everyday Brazilian Portuguese, mercado often refers to a place where you buy groceries, and in many situations it can function a lot like supermarket in casual speech.

If someone wants to be more specific, they might say:

• supermercado = supermarket
• mercado municipal = municipal market
• feira = open-air market / street market

So mercado is a practical, common everyday word, and its exact meaning depends on the situation.