O presente foi uma surpresa para minha irmã.

Here, presente means gift.

In Portuguese, presente can mean:

• gift / present
• present as the current time
• present as an adjective, meaning present / حاضر / in attendance

In O presente foi uma surpresa para minha irmã, the meaning is clearly the gift.

O is the masculine singular definite article, meaning the.

So:

• o presente = the gift

Portuguese uses definite articles more often than English does, so seeing o / a / os / as before nouns is very normal.

Yes, in this sentence presente is masculine, which is why it takes o:

• o presente

You often tell a noun’s gender by the article that goes with it:

• o = masculine singular
• a = feminine singular

Even though presente ends in -e, which does not always clearly show gender, the article tells you that it is masculine here.

Foi is the preterite form of ser, meaning was in the sense of a completed event or fact.

• foi = was / turned out to be
• era = was in the sense of an ongoing background situation, habitual state, or description

In this sentence, foi uma surpresa sounds like a completed reaction or result:

• The gift was a surprise for my sister

If you said era uma surpresa, it would sound more like background description, and it is less natural in this context.

Foi is the third person singular preterite of ser.

That means it matches o presente (the gift) and expresses a completed past event.

A few common forms of ser in the preterite are:

• eu fui = I was
• você/ele/ela foi = you/he/she was
• nós fomos = we were
• eles/elas foram = they were

Because surpresa is being used here as a noun:

• uma surpresa = a surprise

So the structure is:

• foi uma surpresa = was a surprise

Without the article, it would usually sound incomplete or less natural in this sentence.

Also note that surpresa is feminine, so it takes uma:

• uma surpresa

Yes, both can be possible, but they are not exactly the same in feel.

• para minha irmã = for my sister
• foi uma surpresa para minha irmã = the gift was surprising for/to my sister

This is a very natural way to say it.

You may also hear:

• foi uma surpresa à minha irmã

But with surpresa, para is very common and straightforward in Brazilian Portuguese.

So for a learner, para minha irmã is the safest and most natural choice here.

In Brazilian Portuguese, both are possible:

• para minha irmã
• para a minha irmã

The article before a possessive (meu, minha, seu, nossa, etc.) is often optional in Brazilian Portuguese, though usage varies by region, register, and personal style.

So:

• minha irmã = my sister
• a minha irmã = also my sister

In this sentence, para minha irmã sounds perfectly natural.

It literally means:

• minha = my
• irmã = sister

So:

• minha irmã = my sister

Notice that irmã is feminine, and minha agrees with it:

• meu irmão = my brother
• minha irmã = my sister

Because it agrees with the noun it describes.

• irmão is masculine → meu irmão
• irmã is feminine → minha irmã

So minha is the feminine singular form of my.

A rough pronunciation is eer-MAHN, but with a nasal sound at the end.

Important points:

• The ir sounds somewhat like eer
• The stressed syllable is the last one: mã
• ã is nasal, so it is not a plain a

The final sound is not exactly like English ma. Air comes through the nose a bit. Listening and repeating native audio is especially helpful for words with ã.

Yes, but the original order is the most neutral and natural:

• O presente foi uma surpresa para minha irmã.

You could also say:

• Para minha irmã, o presente foi uma surpresa.

That version adds emphasis to for my sister.

So Portuguese word order can be flexible, but the original sentence is the standard choice.

Here it is a noun.

• uma surpresa = a surprise

It can also be used as an adjective in other contexts, for example:

• Ela ficou surpresa. = She was surprised.

So:

• surpresa after uma = noun
• surpresa describing a person = adjective

In your sentence, it is definitely a noun.