A l'hivern, la meva germana acostuma a portar un jersei gris i guants.

Yes. A l'hivern means in winter or in the winter.

Catalan often uses a with seasons in expressions like this:

• a l'estiu = in summer
• a la tardor = in autumn
• a la primavera = in spring
• a l'hivern = in winter

So even though English uses in, Catalan commonly uses a here.

Because hivern is a masculine singular noun, so its normal article is el. But before a word beginning with a vowel sound, el contracts to l'.

So:

• el llibre = the book
• l'hivern = the winter

Also, the h in Catalan is silent, so hivern behaves as if it began with a vowel.

No. In standard Catalan, h is silent.

So hivern is pronounced as if it began with i. That is why you get l'hivern.

The comma separates the time expression from the main part of the sentence.

So the structure is:

• A l'hivern, = in winter
• la meva germana acostuma a portar... = my sister usually wears...

This comma is natural when a time phrase comes first, though punctuation can vary a little depending on style.

Because Catalan normally uses the definite article with possessives.

So:

• la meva germana = my sister
• el meu germà = my brother
• la seva mare = his/her mother

This is different from English, where my sister does not need the.

In some special contexts, especially with family terms in direct address or certain fixed expressions, the article may be left out, but la meva germana is the normal standard form here.

Acostumar a + infinitive means to usually do something, to tend to do something, or to be in the habit of doing something.

So:

• acostuma a portar = usually wears / tends to wear

It describes a habitual action, not just what she is wearing right now.

Compare:

• porta un jersei = she is wearing / she wears a sweater
• acostuma a portar un jersei = she usually wears a sweater

Yes. Sol portar is also a very common way to say usually wears.

So these are both possible:

• La meva germana acostuma a portar un jersei gris i guants.
• La meva germana sol portar un jersei gris i guants.

The meaning is very similar. Acostumar a can feel a bit more like to be accustomed to / to be in the habit of, while sol is often a very direct equivalent of usually.

Yes, portar can mean to carry, but it is also the normal verb for to wear in Catalan.

So:

• portar una bossa = to carry a bag
• portar un jersei = to wear a sweater
• portar ulleres = to wear glasses

This is very common and completely natural in Catalan.

Because Catalan often omits the indefinite article in the plural when the meaning is general or non-specific.

So:

• un jersei gris = a grey sweater
• guants = gloves / some gloves

You could say uns guants, but guants is very natural here and often sounds more neutral.

English behaves differently because it also allows bare plurals:

• a grey sweater and gloves

So this part is actually fairly similar to English.

Because in Catalan, most descriptive adjectives normally come after the noun.

So:

• un jersei gris = a grey sweater
• una casa gran = a big house
• un cotxe vermell = a red car

This is one of the most common adjective patterns in Catalan. Some adjectives can come before the noun, but color adjectives like gris usually come after it.

Yes, jersei is a standard and very common Catalan word for sweater or jumper.

Depending on region, learners may also come across other clothing words, but jersei is widely understood and perfectly normal.

The sentence follows a very typical Catalan structure:

A l'hivern,
time expression

la meva germana
subject

acostuma a portar
verb phrase

un jersei gris i guants
object / thing worn

So the overall order is basically: time + subject + verb + object

That is very natural in Catalan and fairly close to normal English word order.