Hoje comprei um kiwi e uma banana.

Because Portuguese often drops the subject pronoun when the verb form already makes the subject clear.

Here, comprei means I bought, so eu is not necessary.

• (Eu) comprei = I bought
• The -ei ending shows it is first person singular

You could say Hoje eu comprei um kiwi e uma banana, but in normal Portuguese, especially when the subject is obvious, leaving out eu is very common.

Comprei is the pretérito perfeito simples, which is the normal past tense used for a completed action.

It comes from the verb comprar = to buy.

So:

• compro = I buy / I am buying
• comprei = I bought

In this sentence, it tells us that the buying happened today and is seen as a finished action.

Because Portuguese nouns have grammatical gender.

• kiwi is treated as masculine: um kiwi
• banana is feminine: uma banana

So the indefinite article must match the noun:

• um = masculine a/an
• uma = feminine a/an

This is a very common thing English speakers need to get used to, because English does not usually assign grammatical gender to nouns like this.

Unfortunately, you often just have to learn the gender together with the noun.

With kiwi, the usual form is:

• o kiwi
• um kiwi

With banana, it is:

• a banana
• uma banana

A good habit is to memorize new nouns with their article, for example:

• o kiwi
• a banana

That way, you learn the gender automatically.

Hoje means today, and it is an adverb of time. In Portuguese, adverbs of time can go in different places, but putting Hoje at the beginning is very natural.

So these are all possible:

• Hoje comprei um kiwi e uma banana.
• Comprei hoje um kiwi e uma banana.
• Comprei um kiwi e uma banana hoje.

They are all understandable, but starting with Hoje often sounds very natural when you want to set the time first.

Usually, no.

In a short, simple sentence like this, Portuguese normally writes:

• Hoje comprei um kiwi e uma banana.

not:

• Hoje, comprei um kiwi e uma banana.

A comma after Hoje is not normally needed here. You might sometimes see commas used for special emphasis or style, but in ordinary writing, no comma is the standard choice.

Because in Portuguese it is very normal to use an article with each noun when listing separate items.

So:

• um kiwi e uma banana = one kiwi and one banana

This sounds natural and standard. In some cases, Portuguese can omit repeated articles, but here repeating them is the most normal way to say it.

In European Portuguese, Hoje is pronounced roughly like OH-zhuh, but the final vowel is very reduced.

A more accurate idea is:

• ho- sounds like oh
• -je has the zh sound, like the s in measure
• the final vowel is weak, almost like a very short uh or ih

So it is not pronounced like English hoy-jay.

Also, the h in Portuguese is silent, so Hoje does not begin with an English h sound.

In European Portuguese, comprei sounds roughly like kohm-PRAY, though that is only an approximation.

A few useful points:

• The stress is on the last part: -prei
• The m in com- nasalizes the vowel, so it is not a fully pronounced English m
• The r in pr is a tapped sound, not a strong English r

So an English speaker should aim for something like kõ-PRAY, with a nasal first syllable.

In connected speech, e and uma often flow together very smoothly.

• e normally means and
• Before a following vowel, it can sound closer to ee and link into the next word

So e uma may sound a bit like ee-oo-ma or even glide together more tightly in natural speech.

This kind of linking is very common in Portuguese, especially in European Portuguese, where unstressed vowels are often reduced.

Yes, that is grammatically correct.

For example:

• Eu comprei um kiwi e uma banana hoje.
• Comprei um kiwi e uma banana hoje.
• Hoje comprei um kiwi e uma banana.

All of these work. The differences are mostly about focus and style:

• Hoje... puts the time first
• Eu... adds emphasis to the subject
• leaving out eu sounds very natural when the subject is obvious

Yes, this sentence is perfectly natural in Portugal:

• Hoje comprei um kiwi e uma banana.

A native speaker might also say similar things such as:

• Hoje comprei kiwi e banana.
• Comprei um kiwi e uma banana hoje.

But your original sentence is completely normal, clear, and idiomatic. It is a good example of everyday European Portuguese.

It can mean different things depending on context, just like in English.

Kiwi can refer to:

• the fruit
• a kiwi bird
• a person from New Zealand

But in this sentence, because it appears with banana and with the verb comprei, the meaning is clearly the fruit.

So learners should not worry here: the context makes it obvious.