Vão construir uma ponte.

It is the very common Portuguese future construction ir + infinitive:

• vão = they go / they are going
• construir = to build

Together, vão construir means are going to build. In many contexts, it can also be translated naturally as will build.

In European Portuguese, this structure is extremely common in everyday speech.

Because it is the 3rd person plural form of the verb ir (to go):

• eu vou
• tu vais
• ele/ela vai
• nós vamos
• eles/elas vão

So vão construir literally matches they are going to build.

Portuguese often leaves out subject pronouns when the verb already shows who the subject is. This is called a pro-drop language.

So:

• Eles vão construir uma ponte.
• Vão construir uma ponte.

Both are grammatical, and both can mean the same thing. The second version is very natural because vão already tells you the subject is plural.

Here it expresses a future action, not literal movement.

When ir is followed by an infinitive, it usually forms a future meaning:

• Vão construir uma ponte. = They are going to build a bridge.

It does not normally mean that they are physically going somewhere in order to build it.

Because Portuguese uses ir + infinitive directly, with no preposition in between.

So Portuguese says:

• vão construir

not something like:

• vão a construir for this meaning

This is different from English going to build and also different from Spanish, which uses ir a + infinitive.

Because in this structure, only ir is conjugated. The main verb stays in the infinitive:

• vão construir
• vamos construir
• vai construir

So the person and number are shown by ir, not by construir.

Yes. Construirão uma ponte is the simple future of construir, and it also means They will build a bridge.

The difference is mainly one of style and tone:

• Vão construir uma ponte = very common in everyday speech, often sounds more immediate or planned
• Construirão uma ponte = more formal, more written, sometimes more detached

In spoken European Portuguese, vão construir is usually the more natural choice.

Uma is the feminine singular indefinite article, meaning a or one.

So:

• uma ponte = a bridge

The noun ponte is feminine, so the article must also be feminine:

• a ponte = the bridge
• uma ponte = a bridge

Because ponte is simply a feminine noun in Portuguese. Grammatical gender is something you usually have to learn with each noun.

So you say:

• a ponte
• uma ponte

not:

• o ponte
• um ponte

This grammatical gender does not mean the bridge is biologically female; it is just part of how the noun works in Portuguese.

Yes, in theory it could, because vão is also the verb form used with vocês.

So depending on context:

• Vocês vão construir uma ponte. = You all are going to build a bridge.
• Eles vão construir uma ponte. = They are going to build a bridge.

Without a subject pronoun, they is often the most likely interpretation, but context decides.

The tricky part is ão, which is a very common Portuguese nasal ending.

A rough guide:

• v as in English v
• ão is nasal, not a plain ow

So vão is approximately like vown said through the nose, but that is only an approximation.

In European Portuguese, the nasal quality is very important. The accent mark in vão helps show the stressed nasal sound.

In European Portuguese, the usual way is:

• Estão a construir uma ponte.

That is different from:

• Vão construir uma ponte. = They are going to build a bridge

So:

• estão a construir = action in progress now
• vão construir = future or planned action

This is an important distinction in European Portuguese.