A praça onde nos encontramos na sexta-feira estava vazia por causa da chuva.

Onde means where and is used for places. In A praça onde nos encontramos..., it introduces a relative clause describing a praça.

So:

• a praça = the square / plaza
• onde nos encontramos = where we met

You could also say em que:

• A praça em que nos encontramos...

That is also correct, but onde is more natural here because the noun it refers to is a place.

Here nos means each other / ourselves. With encontrar(-se), Portuguese can express the idea of people meeting one another.

So nos encontramos means:

• we met
• literally something like we found each other / we met ourselves

Without nos, encontramos would usually mean we found something:

• Encontramos a chave. = We found the key.

In this sentence, nos encontramos is the natural way to say we met.

It is the pretérito perfeito (simple past / preterite) of encontrar-se.

• eu me encontrei
• você se encontrou
• nós nos encontramos

Here it refers to a completed event in the past: the meeting happened on Friday.

So:

• nos encontramos na sexta-feira = we met on Friday

In Brazilian Portuguese, object pronouns like me, te, se, nos often come before the verb, especially in everyday language.

So onde nos encontramos is the normal Brazilian pattern.

This placement is called proclisis. Relative words like onde commonly attract the pronoun before the verb.

In European Portuguese, you may more often see forms like encontrámo-nos in some contexts, but in Brazilian Portuguese nos encontramos is much more natural.

Na is a contraction of:

• em + a = na

So:

• na sexta-feira literally means on the Friday
• in natural English, this is just on Friday

Portuguese often uses an article with days of the week when talking about a specific day:

• na sexta-feira = on Friday

If you were speaking more generally or habitually, the structure could change:

• às sextas-feiras = on Fridays / every Friday

In Portuguese, the weekday names from Monday to Friday are normally written with a hyphen:

• segunda-feira
• terça-feira
• quarta-feira
• quinta-feira
• sexta-feira

This is just the standard spelling.

Estava is from estar, which is used here to describe a temporary state or condition:

• A praça estava vazia = the square was empty

That sounds natural because emptiness is being presented as a situation at that moment, especially because of the rain.

If you used era, it would sound more like a characteristic or defining quality, which is less natural here.

So:

• estava vazia = was empty at that time
• era vazia = was an empty kind of place / was empty by nature or character

Estava is the imperfect of estar. It is used because the sentence is describing the background condition of the square at that time.

Portuguese often uses:

• preterite for completed actions
• imperfect for descriptions, ongoing situations, or background information

Here that contrast appears clearly:

• nos encontramos = completed event: we met
• estava vazia = background description: it was empty

That is a very common and important pattern in Portuguese.

Because adjectives in Portuguese usually agree with the noun in gender and number.

• praça is feminine singular
• so the adjective must also be feminine singular: vazia

Compare:

• o parque estava vazio = the park was empty
• a praça estava vazia = the square was empty

Por causa de is a fixed expression meaning because of.

So:

• por causa da chuva = because of the rain

The final da is a contraction:

• de + a = da

So the full structure is:

• por causa de a chuva → por causa da chuva

This expression is followed by a noun:

• por causa do trânsito = because of the traffic
• por causa da chuva = because of the rain

If you want to say because followed by a full clause, Portuguese usually uses porque:

• A praça estava vazia porque estava chovendo.

Portuguese very often contracts prepositions with definite articles.

Two very common ones are:

• em + a = na
• de + a = da

So in this sentence:

• na sexta-feira = em a sexta-feira
• da chuva = de a chuva

Other common contractions are:

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

These contractions are standard and usually required.

Portuguese uses definite articles more often than English does.

Here A praça means the square and refers to a specific square, the one where the meeting happened.

Using the article sounds natural because the noun is specific and identifiable from the context.

Yes. That is correct.

Possible versions include:

• A praça onde nos encontramos...
• A praça em que nos encontramos...
• A praça na qual nos encontramos...

All are grammatical, but they differ a little in style:

• onde = most natural and common for places
• em que = correct, slightly more neutral/formal
• na qual = more formal or written

For everyday Brazilian Portuguese, onde is usually the best choice here.

Because Portuguese often drops subject pronouns when the verb ending already shows who the subject is.

• encontramos already tells you the subject is we
• so nós is not necessary

You could say:

• onde nós nos encontramos

But that would usually add emphasis or contrast. In a normal sentence, leaving out nós is more natural.

Usually in a sentence like this, na sexta-feira means on Friday, referring to one specific Friday.

If you want to talk about a repeated habit, Portuguese normally uses:

• às sextas-feiras = on Fridays / every Friday

So compare:

• nos encontramos na sexta-feira = we met on Friday
• nos encontramos às sextas-feiras = we meet on Fridays

Because this relative clause is identifying which square is being talked about.

• A praça onde nos encontramos... = the square where we met

This is a restrictive relative clause, so no comma is normally used.

If the square were already clearly identified and the clause were just extra information, a comma could appear in some contexts. But in this sentence, the clause helps specify the noun, so no comma is the normal choice.