Antes de criticar alguém, é melhor ouvir com calma.

Because antes de is the normal structure for before when it is followed by a verb.

• antes de + infinitive = before doing something
• antes de criticar = before criticizing

A few similar examples:

• antes de sair = before leaving
• antes de falar = before speaking
• antes do jantar = before dinner

Notice that with a noun, de often combines with the article:

• de + o = do
• antes do jantar

It is in the infinitive because after antes de, Portuguese normally uses the infinitive when talking about an action in a general way.

So:

• antes de criticar alguém = before criticizing someone

This sentence is giving general advice, not speaking about one specific person, so the plain infinitive criticar fits well.

In European Portuguese, you can also use the personal infinitive if you want to make the subject more specific:

• Antes de criticares alguém... = Before you criticize someone...

That version sounds more directly addressed to you. The original sentence is more general and impersonal.

Alguém means someone or somebody.

It is an indefinite pronoun, so it refers to a person without naming who that person is.

Examples:

• Vi alguém à porta. = I saw someone at the door.
• Não conheço alguém assim. = I do not know anyone like that.
  In negative contexts, English often uses anyone, but Portuguese may still use alguém less commonly depending on structure; very often ninguém or other wording is preferred.

In your sentence, alguém is simply someone:
Antes de criticar alguém... = Before criticizing someone...

The comma separates the introductory part of the sentence from the main statement.

• Antes de criticar alguém = introductory clause
• é melhor ouvir com calma = main clause

So the comma helps the sentence breathe naturally:

• Antes de criticar alguém, é melhor ouvir com calma.

In short, it works a lot like English punctuation in a sentence such as:

• Before criticizing someone, it is better to listen calmly.

Literally, é melhor means is better, but in this kind of sentence it works like the English expression it is better to...

So:

• é melhor ouvir = it is better to listen

This is a very common Portuguese structure:

• É importante estudar. = It is important to study.
• É difícil explicar isso. = It is difficult to explain that.
• É melhor esperar. = It is better to wait.

There is no expressed subject like English it. Portuguese often uses this kind of impersonal structure without needing a separate subject word.

Because Portuguese does not need a dummy subject like English it in expressions of this type.

English says:

• It is better to listen.

Portuguese simply says:

• É melhor ouvir.

The verb is still there, but Portuguese leaves out that empty subject that English requires.

This is very common:

• É tarde. = It is late.
• É bom descansar. = It is good to rest.
• É preciso estudar. = It is necessary to study.

It can mean either, depending on context.

In this sentence, it clearly means listen, because the idea is to pay attention before criticizing someone.

Examples:

• Ouvi um barulho. = I heard a noise.
• Ouço música todos os dias. = I listen to music every day.

So Portuguese does not always separate hear and listen as strictly as English does. Context tells you which meaning is intended.

Both ouvir and escutar can mean to listen, and in many cases they are close in meaning.

In European Portuguese:

• ouvir is extremely common in everyday language
• escutar can sometimes sound a bit more deliberate, like listen carefully

So in this sentence, ouvir sounds very natural.

You could also say:

• Antes de criticar alguém, é melhor escutar com calma.

That is understandable, but ouvir com calma feels very natural and idiomatic.

Because com calma is a very common and natural way to say calmly, patiently, or without rushing.

So:

• ouvir com calma = listen calmly / listen patiently / listen without rushing

You could say calmamente, and it is grammatically correct, but com calma often sounds more natural in everyday Portuguese.

Compare:

• Fala com calma. = Speak calmly / Take it easy when speaking.
• Lê com calma. = Read carefully / Read without rushing.

So com calma is not just about emotional calm; it often suggests taking time and being patient.

The object is understood from the context.

The sentence means that before criticizing someone, it is better to listen calmly — in other words, to listen to that person, or at least to what they have to say.

Portuguese often leaves out an object when it is obvious.

If you wanted to make it explicit, you could say:

• Antes de criticar alguém, é melhor ouvi-lo com calma.
• Antes de criticar alguém, é melhor ouvi-la com calma.
• Antes de criticar alguém, é melhor ouvir essa pessoa com calma.

But the original version sounds natural because the listener can easily understand who is being referred to.

Yes. That is a very useful European Portuguese point.

Criticares is the personal infinitive, and it can be used after prepositions when the subject is clear.

So:

• Antes de criticar alguém... = before criticizing someone / general statement
• Antes de criticares alguém... = before you criticize someone

If you use the more specific criticares, the rest of the sentence would often also become more personal:

• Antes de criticares alguém, é melhor ouvires com calma.

That sounds like direct advice to you.

The original sentence is more general and impersonal, which is why it uses the plain infinitive.

Because é and e are different words.

• é = is
• e = and

So in your sentence:

• é melhor = is better

Without the accent, e melhor would mean and better, which is a completely different thing.

This is one of the most important little accents to notice in Portuguese.

It sounds natural and neutral.

It works well as:

• everyday advice
• a proverb-like statement
• something you might read or hear in normal speech or writing

It is neither overly formal nor unusually casual. It is the kind of sentence a native speaker in Portugal could naturally say.