Quan el meu germà truca al timbre, la meva mare baixa al portal.

In Catalan, it is very common to use the definite article before a possessive:

• el meu germà
• la meva mare

This is especially normal with family members and many everyday nouns. So Catalan usually says the my brother / the my mother in a way that sounds natural in Catalan, even though English does not do that.

If you leave out the article, it can sound literary, old-fashioned, or stylistically marked in many contexts.

Quan means when, but in this sentence it often has the sense of whenever.

Because both verbs are in the present tense, the sentence usually describes something habitual or repeated:

• Whenever my brother rings the doorbell, my mother goes down to the entrance.

So quan can introduce:

• a specific time: when
• a repeated situation: whenever

Here, the repeated meaning is the most likely one.

Catalan uses the present tense for habitual actions, just like English does:

• Quan el meu germà truca al timbre, la meva mare baixa al portal.

This means that this is what usually happens.

So:

• truca = rings / does ring
• baixa = goes down

Depending on context, Catalan present can sometimes also refer to the future, but without extra context this sentence is most naturally understood as a regular, repeated action.

Yes, trucar often means to call or to phone.

But in expressions like trucar al timbre, it means to ring the bell / ring the doorbell.

So here:

• truca al timbre = rings the doorbell

This is one of those cases where a verb has more than one common use depending on the expression.

Because a + el contracts to al in Catalan.

So:

• a + el timbre → al timbre
• a + el portal → al portal

This is a very common contraction.

Another one you will often see is:

• de + el → del

For example:

• del portal

In this kind of sentence, portal usually means the entrance area of a building, especially an apartment building.

Depending on context, English might translate it as:

• entrance
• entryway
• lobby
• front entrance

So baixar al portal suggests that the mother goes downstairs to the building entrance to open the door or meet the brother.

It does not mean a fantasy-style portal.

Yes. Baixar means to go down, to come down, or to go downstairs, depending on context.

Here it suggests that the mother is upstairs in the apartment, and she goes down to the building entrance:

• la meva mare baixa al portal = my mother goes down to the entrance

Catalan often uses a verb of movement very literally here, where English might choose different wording depending on the situation.

Catalan often leaves out subject pronouns because the verb form usually makes the subject clear, or the subject noun is already stated.

Here the subjects are already explicit:

• el meu germà truca
• la meva mare baixa

So adding ell or ella would usually be unnecessary.

Catalan is a language where dropping the subject pronoun is very normal.

The possessive agrees with the noun it goes with.

So:

• germà is masculine singular → el meu germà
• mare is feminine singular → la meva mare

The possessive changes form like this:

• meu = masculine singular
• meva = feminine singular
• meus = masculine plural
• meves = feminine plural

So the form depends on the possessed noun, not on the speaker.

Yes, it is the normal punctuation here.

The first part is a subordinate clause introduced by quan:

• Quan el meu germà truca al timbre, ...

Then the main clause follows:

• la meva mare baixa al portal.

The comma helps separate those two parts clearly. It is especially natural when the quan clause comes first.

Yes. You can also say:

La meva mare baixa al portal quan el meu germà truca al timbre.

This means the same thing.

The main difference is word order:

• Quan... , ... = time clause first
• ..., quan... = main clause first

When the quan clause comes second, the comma is often omitted.

Yes, it can, depending on context.

For example, if people are waiting at home and expecting the brother, this could mean:

• When my brother rings the doorbell, my mother goes down to the entrance.

In English, you might sometimes prefer will go down, but Catalan often keeps the present tense in this kind of time clause structure.

So the sentence can mean either:

• a usual repeated action, or
• a specific expected event

Context tells you which one is intended.