O motorista abriu o porta-malas para colocar as sacolas do supermercado.

In Portuguese, it is very common to use the definite article before a noun when talking about a specific person or thing.

• o motorista = the driver
• motorista by itself can mean driver in a more general or dictionary-style sense

Here, O motorista tells us we are talking about a specific driver.

Motorista is one of those Portuguese nouns that often keeps the same form for both masculine and feminine. The article changes to show gender:

• o motorista = the male driver
• a motorista = the female driver

So in this sentence, o tells you the driver is male.

Abriu is the preterite form of the verb abrir (to open). The preterite is used for a completed action in the past.

• abrir = to open
• ele abriu = he opened

So O motorista abriu means The driver opened.

Portuguese usually uses articles more often than English does. Since this is a specific trunk, o porta-malas is natural.

• abriu o porta-malas = opened the trunk

Leaving out the article would sound unnatural in this sentence.

Good question. Porta-malas is a fixed compound noun meaning trunk or car boot. Even though porta by itself is feminine, the compound noun is treated as masculine:

• o porta-malas

You should learn porta-malas as one complete word/expression, not by trying to assign gender from porta alone.

In this sentence, porta-malas is singular.

Some Portuguese nouns have the same form in the singular and plural. Porta-malas is one of them.

• singular: o porta-malas
• plural: os porta-malas

So the article tells you whether it is singular or plural.

Para often means for or in order to, and colocar means to put/place.

So:

• para colocar = to put / in order to put

In this sentence, it expresses purpose:

• abriu o porta-malas para colocar...
• he opened the trunk to put...

Because it follows para to express purpose. In Portuguese, para + infinitive is a very common structure.

Examples:

• Estudo para aprender. = I study to learn.
• Abriu o porta-malas para colocar as sacolas. = He opened the trunk to put the bags in.

So colocar stays in the infinitive because it is linked to para.

Both can mean to put.

• colocar = to put/place
• pôr = to put

In many contexts, they are interchangeable. Colocar is often felt to be a little more straightforward for learners because its forms are more regular. In this sentence, both would work:

• para colocar as sacolas
• para pôr as sacolas

But colocar is very common and natural.

Because sacolas is a feminine plural noun.

• singular: a sacola = the bag
• plural: as sacolas = the bags

The article and noun must agree in gender and number:

• feminine singular: a sacola
• feminine plural: as sacolas

Do is a contraction of:

• de + o = do

So:

• do supermercado = from the supermarket / of the supermarket

In this sentence, as sacolas do supermercado means the supermarket bags or more naturally the bags from the supermarket.

Yes, grammatically it could mean the supermarket’s bags, but in normal everyday usage here it usually means shopping bags from the supermarket.

So a native speaker will normally understand:

• as sacolas do supermercado = the grocery bags / the shopping bags from the supermarket

Context makes this very natural.

Because porta-malas is already the object being opened, and the sentence focuses on opening it to put the bags inside. Portuguese often leaves the destination implied when it is obvious from context.

So:

• abriu o porta-malas para colocar as sacolas do supermercado

naturally means:

• he opened the trunk to put the grocery bags in it

If you wanted to be more explicit, you could say:

• ...para colocar as sacolas no porta-malas

But it is not necessary here.

The basic structure is:

• O motorista = subject
• abriu = verb
• o porta-malas = direct object
• para colocar as sacolas do supermercado = purpose phrase

So the pattern is roughly:

Subject + Verb + Object + Purpose

This is a very common and natural Portuguese word order.