Eu quero comprar um sanduíche de queijo hoje.

Because Portuguese often uses querer + infinitive to say to want to do something.

• quero = I want
• comprar = to buy

So quero comprar literally means I want to buy.

This is very similar to English:

• I want to eat
• I want to go
• I want to buy

In Portuguese:

• quero comer
• quero ir
• quero comprar

Yes. In Brazilian Portuguese, subject pronouns are often omitted when the verb already makes the subject clear.

So both of these are natural:

• Eu quero comprar um sanduíche de queijo hoje.
• Quero comprar um sanduíche de queijo hoje.

The version with eu can sound a little more explicit or emphatic, but both are correct.

Because sanduíche is a masculine noun in Portuguese, so it takes the masculine indefinite article um.

• um sanduíche
• not uma sanduíche

This is a grammar point English speakers often need to get used to: nouns in Portuguese have grammatical gender, and articles must agree with the noun.

In Portuguese, food types are often formed with de + ingredient/filling.

So:

• sanduíche de queijo = cheese sandwich
• pizza de queijo = cheese pizza
• pastel de queijo = cheese pastry

Here, de does not mean possession. It describes what kind of sandwich it is, or what it contains.

This is one of those places where Portuguese and English structure things differently.

Because in expressions like sanduíche de queijo, the noun after de is being used in a general, descriptive way.

So:

• de queijo = of cheese / cheese-filled / cheese-type
• not do queijo

If you said do queijo, it would usually mean something more specific, like of the cheese or from the cheese, which does not fit here.

This article-free pattern is very common with food:

• sanduíche de presunto
• pizza de calabresa
• pastel de carne

You could, but it would not mean exactly the same thing.

• sanduíche de queijo = a cheese sandwich as a type of sandwich
• sanduíche com queijo = a sandwich with cheese in it

So de queijo is the more natural choice if you are naming the sandwich itself.
Com queijo sounds more like you are describing one of its ingredients.

Yes, hoje can move around in the sentence. Portuguese has fairly flexible word order with time expressions.

These are all possible:

• Eu quero comprar um sanduíche de queijo hoje.
• Hoje eu quero comprar um sanduíche de queijo.
• Eu hoje quero comprar um sanduíche de queijo.

The version with hoje at the end sounds very natural and neutral.

Putting hoje at the beginning can give it a bit more emphasis, like:

• Today, I want to buy a cheese sandwich.

It is correct and natural if you really mean buy.

But depending on the situation, Brazilians might choose a different verb:

• comprar = to buy
• pedir = to order
• pegar = to get
• fazer = to make

For example:

• At a bakery: Quero comprar um sanduíche de queijo.
• At a café table: Quero pedir um sanduíche de queijo.
• If you are preparing it yourself: Quero fazer um sanduíche de queijo.

So comprar is fine, but context matters.

A good approximate pronunciation for English speakers is:

san-doo-EE-shee

The stressed part is the uí area, which is why the word has an accent: sanduíche.

A few useful notes:

• ã/san has a nasal sound
• ch in Brazilian Portuguese usually sounds like sh
• the final e is often pronounced like ee

You do not need perfect pronunciation right away, but the important part is not to pronounce it exactly like English sandwich.

Yes, sanduíche is common and widely understood in Brazil.

However, you may also hear related words depending on the context:

• lanche = snack / light meal; sometimes used more broadly
• misto-quente = grilled ham-and-cheese sandwich
• hambúrguer = hamburger

So sanduíche is correct and natural, but lanche is also a very common everyday word in Brazilian Portuguese. Just remember that lanche is broader than sandwich.

Not always, but in this sentence it sounds natural.

• quero comprar um sanduíche de queijo = I want to buy a cheese sandwich

If you remove um, the sentence can sound less complete in standard usage.

Portuguese usually uses an article where English also would:

• a sandwich = um sanduíche

In some contexts, a speaker might shorten things in casual speech, but for learners, using um here is the safest and most natural choice.

Then you would use the definite article o:

• Eu quero comprar o sanduíche de queijo hoje.

That means I want to buy the cheese sandwich today.

So:

• um sanduíche = a sandwich
• o sanduíche = the sandwich

This article difference is very important in Portuguese, just as it is in English.