A minha irmã cozinha lentilhas para o jantar.

In European Portuguese, it is very common to use the definite article before a possessive: a minha irmã, o meu pai, a nossa casa, etc.

So a minha irmã is the most natural form in Portugal.

You can sometimes hear or see the article omitted, but for a learner of European Portuguese, it is safest to learn that possessive + noun usually takes the article.

Examples:

• o meu irmão
• a tua amiga
• os nossos pais

Because it agrees with irmã, which is a feminine noun.

In Portuguese, possessives agree with the thing possessed, not with the owner.

So:

• a minha irmã — feminine singular
• o meu irmão — masculine singular
• as minhas irmãs — feminine plural
• os meus irmãos — masculine plural

Here, cozinha is a verb.

It comes from cozinhar (to cook), and cozinha is the 3rd person singular present form:

• eu cozinho
• tu cozinhas
• ele/ela/você cozinha

So in this sentence, cozinha means cooks.

This can confuse learners because cozinha can also be the noun kitchen. The difference comes from context:

• A minha irmã cozinha lentilhas → verb
• A cozinha é grande → noun

If it were the noun, you would usually expect an article or another clue before it.

Grammatically, cozinha is the simple present, so its basic meaning is cooks.

But like in many languages, the present tense can sometimes sound broader depending on context. In practice:

• A minha irmã cozinha lentilhas can mean she cooks lentils, or she is cooking lentils, depending on the situation.
• If you want to be very explicit about an action happening right now in European Portuguese, you would often say está a cozinhar.

Example:

• A minha irmã está a cozinhar lentilhas. — she is cooking lentils right now

So the sentence with cozinha is normal, but está a cozinhar is the more specifically ongoing form in Portugal.

Because lentilhas is being used here in a general or indefinite way, like lentils in English.

Portuguese often leaves out the article with direct objects when talking about something in a general sense:

• comer arroz
• beber água
• comprar pão
• cozinhar lentilhas

If you said as lentilhas, it would usually sound more specific, like the lentils:

• A minha irmã cozinha as lentilhas que comprámos ontem.

So in your sentence, lentilhas simply means lentils in general, not a specific previously identified batch.

Para o jantar means for dinner.

It tells you the purpose of the cooking: the lentils are being cooked for the evening meal.

Breakdown:

• para = for
• o jantar = the dinner / dinner meal

So para o jantar means something like for dinner or for the dinner meal.

Yes, para jantar is also possible and very natural.

There is a small difference in feel:

• para jantar = for dinner, in a more general sense
• para o jantar = for the dinner meal, a bit more definite

In many everyday contexts, both work:

• Vou fazer sopa para jantar.
• Vou fazer sopa para o jantar.

In your sentence, para o jantar sounds completely normal.

Because Portuguese can use meal words both with and without the article, depending on structure and style.

For example:

• Janto às oito. — I have dinner at eight.
• O jantar está pronto. — Dinner is ready.
• para jantar — for dinner
• para o jantar — for the dinner meal

So jantar does not always need an article, but it often takes one in certain expressions. In your sentence, para o jantar is perfectly idiomatic.

This is the normal Portuguese order:

subject + verb + object + extra information

So:

• A minha irmã = subject
• cozinha = verb
• lentilhas = direct object
• para o jantar = purpose/complement

This is the most neutral and natural order.

You can move things around for emphasis, but the given order is the standard one.

Yes, Portuguese often allows subject omission because the verb ending already gives information about the subject.

So you could say:

• Cozinha lentilhas para o jantar.

However, without context, that could mean he/she/you formal cooks lentils for dinner, because cozinha can match several subjects.

That is why keeping A minha irmã makes the sentence clearer.

The tricky part is the ã, which is a nasal sound.

A rough guide:

• ir sounds a bit like eer but shorter and less fully pronounced
• mã has a nasal vowel, not a fully pronounced ma

So irmã is approximately: eer-MAN with a nasal ending, but not exactly like English man

Important points:

• the final ã is nasal
• the m is not strongly pronounced as a separate consonant there; it helps nasalise the vowel

Also, in European Portuguese, unstressed vowels are often reduced, so the first part may sound less clear than an English speaker expects.

Because nouns in Portuguese have grammatical gender, and jantar is a masculine noun:

• o jantar

There is no special logic you can always rely on here; gender often just has to be learned with each noun.

So it is good practice to learn nouns together with their article:

• a irmã
• as lentilhas
• o jantar

That way, you automatically learn the correct gender and number.

Yes, it sounds natural.

A speaker from Portugal would understand it immediately, and it is grammatically correct.

A few equally natural alternatives might be:

• A minha irmã faz lentilhas para o jantar.
• A minha irmã está a cozinhar lentilhas para o jantar.

But your original sentence is absolutely fine and natural in European Portuguese.