Eu vou tirar o chapéu antes de entrar no restaurante.

Vou tirar is the very common ir + infinitive future, often called the near future. In Brazilian Portuguese, this is the most natural way to talk about many future actions in everyday speech.

• Eu vou tirar o chapéu = I’m going to take off the hat
• Eu tirarei o chapéu = I will take off the hat

Both are correct, but tirarei sounds more formal, literary, or less conversational. In normal spoken Brazilian Portuguese, vou tirar is much more common.

Here, tirar means to take off or to remove.

So:

• tirar o chapéu = to take off the hat

But tirar is a very broad verb in Portuguese, and its meaning depends on context. It can also mean things like:

• to take out
• to remove
• to get
• to take a photo in some expressions, like tirar uma foto

In this sentence, the meaning is clearly take off.

Portuguese often uses the definite article with clothing, body parts, and personal items when it is already obvious whose item it is.

So tirar o chapéu naturally means take off the hat, and in context it is understood to be my hat.

This is very normal in Portuguese. Compare:

• Vou lavar as mãos. = I’m going to wash my hands.
• Ela tirou os sapatos. = She took off her shoes.

You can say meu chapéu, but it usually adds emphasis, contrast, or clarity:

• Vou tirar meu chapéu, não o seu.

Because antes is normally followed by de when it introduces a verb or a noun phrase.

So:

• antes de entrar = before entering
• antes do jantar = before dinner

You should think of antes de as a fixed pattern.

Correct:

• antes de entrar no restaurante

Not standard:

• antes entrar no restaurante

It is in the infinitive because the subject of entrar is the same as the subject of the main verb.

In other words:

• Eu vou tirar o chapéu
• and eu is also the one who will entrar

So Portuguese uses:

• antes de entrar = before entering

If you want to state the subject explicitly, especially if it is different, you can say:

• antes de eu entrar no restaurante = before I enter the restaurant
• antes de ele entrar no restaurante = before he enters the restaurant

But when the subject is the same and obvious, antes de entrar is the most natural choice.

No is a contraction of:

• em + o = no

So:

• no restaurante = in the restaurant / into the restaurant, depending on context

Here, with entrar, it means into the restaurant.

Other common contractions:

• na = em + a
• nos = em + os
• nas = em + as

Examples:

• na escola
• no carro
• nos hotéis
• nas lojas

In standard Brazilian Portuguese, entrar is usually used with em:

• entrar no restaurante
• entrar na sala
• entrar em casa

So no restaurante is the expected form.

For an English speaker, it helps to learn entrar em as the normal pattern in Brazilian Portuguese.

You do not have to say Eu. Portuguese often omits subject pronouns when the meaning is clear from the verb.

So both are correct:

• Eu vou tirar o chapéu antes de entrar no restaurante.
• Vou tirar o chapéu antes de entrar no restaurante.

Including eu can add:

• emphasis
• contrast
• clarity

For example:

• Eu vou tirar o chapéu, mas ele não vai.

Without emphasis, dropping eu is very natural.

Yes. Tirar o chapéu para alguém can be an idiomatic expression meaning something like:

• to take one’s hat off to someone
• to admire or praise someone

Example:

• Tiro o chapéu para ela. = I take my hat off to her.

But in your sentence, the meaning is almost certainly literal, because of the context:

• antes de entrar no restaurante

That sounds like physically removing a hat before going in.

Yes. Portuguese allows some flexibility here.

These are both natural:

• Eu vou tirar o chapéu antes de entrar no restaurante.
• Antes de entrar no restaurante, eu vou tirar o chapéu.

The second version puts more focus on the before entering the restaurant part.

The meaning stays basically the same.

Yes, both are possible, but they mean slightly different things.

• no restaurante = in/into the restaurant
• num restaurante = in/into a restaurant

So:

• antes de entrar no restaurante suggests a specific restaurant, or one already known in context
• antes de entrar num restaurante means before entering a restaurant, more general or nonspecific

Portuguese uses articles very often, so no restaurante is completely normal.

Chapéu is pronounced roughly like sha-PEH-o, with the stress on the second syllable.

A closer approximation is:

• cha-PÉU

The acute accent on é tells you that:

1. that syllable is stressed
2. the vowel is an open é sound

So the stress is not on cha, but on péu.

Also, the ending éu forms a diphthong, so it flows together as one syllable:

• cha-péu

The sentence is correct in both, and it would be understood in both varieties.

That said, it sounds very natural in Brazilian Portuguese because:

• vou + infinitive is extremely common
• entrar no restaurante is standard
• the overall structure is simple and idiomatic

So it is a good, natural sentence for Brazilian Portuguese, and it is also acceptable in European Portuguese.