Minha filha quer usar sandália preta, porque o sapato fechado não é confortável.

Because minha has to agree with filha, the thing being possessed.

In Portuguese, possessive words like meu / minha / meus / minhas agree in gender and number with the noun that follows:

• meu filho = my son
• minha filha = my daughter
• meus filhos = my sons / my children
• minhas filhas = my daughters

So since filha is feminine singular, minha is the correct form.

Yes. In Brazilian Portuguese, both are possible:

• Minha filha quer...
• A minha filha quer...

The article a before a possessive is very common in Brazil, especially in speech. Leaving it out is also correct and often sounds a bit more direct or neutral.

With family words like mãe, pai, filho, filha, omitting the article is especially common.

This is a very common structure in Portuguese.

• quer = wants
• usar = to wear / to use

After a conjugated verb like querer, the next verb normally stays in the infinitive:

• quero comer = I want to eat
• ela quer sair = she wants to go out
• minha filha quer usar = my daughter wants to wear

So quer usar works just like English wants to wear.

Yes. In Portuguese, usar is very commonly used for clothes, shoes, and accessories.

Examples:

• usar sandália = to wear sandals
• usar vestido = to wear a dress
• usar óculos = to wear glasses

Even though usar also means to use, it is perfectly normal for clothing.

Another common verb is vestir, but usar is often more natural for talking about what someone wears, especially items like shoes, accessories, or particular styles.

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

• sandália is feminine singular
• so the adjective becomes preta

Compare:

• sandália preta
• sapato preto
• sandálias pretas
• sapatos pretos

The same happens with sapato fechado:

• sapato is masculine singular
• so fechado is masculine singular too

Yes, but the meaning or feel changes a bit.

After usar, Portuguese often leaves out the article when talking generally about clothing or footwear:

• usar saia
• usar camisa branca
• usar sandália preta

This sounds like talking about the type/style of thing someone wants to wear.

If you say usar uma sandália preta, it sounds more like one particular black sandal item or a more specific instance.

If you say usar a sandália preta, that usually means a specific black sandal already known in the conversation.

So in this sentence, usar sandália preta sounds natural because it focuses on the kind of footwear she wants to wear.

Literally, it means closed shoe, but in natural English it usually refers to a shoe that covers the foot more fully, especially a closed-toe shoe.

It contrasts with open footwear like:

• sandália = sandal
• chinelo = flip-flop / slipper
• sapato fechado = closed shoe

So the idea is that she wants sandals because closed shoes are not comfortable.

Not necessarily.

In Portuguese, the definite article is often used where English might be more general. So o sapato fechado can mean:

• the specific closed shoe being considered, or
• closed shoes as a category in this situation

Portuguese often uses the singular definite form to talk about a type of thing more naturally than English does.

So here o sapato fechado can be understood as closed shoes / closed footwear in general, not only one single shoe.

Because some Portuguese adjectives have the same form for masculine and feminine in the singular.

Confortável is one of them:

• o sapato é confortável
• a sandália é confortável

The form stays the same in both masculine and feminine singular.

Only the plural changes:

• os sapatos são confortáveis
• as sandálias são confortáveis

So preta changes because that adjective has masculine/feminine forms, but confortável does not.

This is about ser vs estar.

• ser is often used for general characteristics
• estar is often used for temporary states or how something is at the moment

Here, não é confortável means the closed shoe is generally not comfortable.

If you said não está confortável, it would sound more like:

• it does not feel comfortable right now
• in this moment or in this situation, it is uncomfortable

So não é confortável is the more natural choice if you mean that this kind of shoe is not comfortable for her.

Because here it means because, introducing the reason.

• porque = because

Portuguese has several similar-looking forms:

• porque = because
• por que = why / for what reason
• por quê = why, usually at the end of a question
• o porquê = the reason

In this sentence, the second part gives the reason, so porque is the correct form.

Not really. In a sentence like this, many people would write it without the comma:

• Minha filha quer usar sandália preta porque o sapato fechado não é confortável.

The comma can appear in real-life writing because speakers may feel a pause there, or they may treat the second part as a stronger explanation. But if you are unsure, leaving the comma out is often the safer default in a straightforward because sentence.