A l'hivern, acostumo a comprar guants negres a la botiga.

This is a very common Catalan way to express a season as a time phrase: a + article + season.

So:

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

Here, hivern starts with a vowel sound, so el becomes l':

• el hivern → l'hivern

That gives a l'hivern.

Because the sentence begins with a fronted time expression. In Catalan, if you move a time phrase like A l'hivern to the beginning for emphasis or topic-setting, a comma is very common.

So:

• A l'hivern, acostumo a comprar... = fronted time phrase
• Acostumo a comprar... a l'hivern = same basic meaning, different word order

The comma helps separate that opening time frame from the rest of the sentence.

Yes. Catalan word order is fairly flexible.

You could also say:

• Acostumo a comprar guants negres a la botiga a l'hivern.

Putting A l'hivern first gives it a bit more prominence, as if you are setting the scene: As for winter...

Acostumo is the 1st person singular present form of acostumar (a), used here to mean:

• I usually
• I tend to
• I am in the habit of

So acostumo a comprar means I usually buy or I tend to buy.

It expresses a habitual action, not something happening right now.

Because this verb pattern requires it.

In this use, Catalan normally has:

• acostumar a + infinitive

Examples:

• Acostumo a llegir al vespre.
• Acostumes a anar-hi sovint?
• Acostumen a menjar tard.

English says I usually buy, without a preposition, but Catalan needs a before the infinitive.

Not in this sentence.

Here, acostumar a + infinitive means to usually do something.

But acostumar-se a usually means to get used to or to become accustomed to.

Compare:

• Acostumo a comprar guants negres. = I usually buy black gloves.
• M'acostumo al fred. = I am getting used to the cold.

So the reflexive form acostumar-se has a different meaning.

Because Catalan often drops subject pronouns when the verb ending already makes the subject clear.

Acostumo ends in -o, which shows I.

So:

• Acostumo a comprar... = perfectly natural
• Jo acostumo a comprar... = also possible, but usually only if you want emphasis or contrast

For example:

• Jo acostumo a comprar guants negres, però ell no.

Because Catalan often uses a bare plural for nonspecific things.

So comprar guants negres means buying black gloves in a general, nonspecific sense.

Compare:

• comprar guants negres = buy black gloves / some black gloves
• comprar els guants negres = buy the black gloves, meaning specific ones already known in the conversation

English does this too in many cases, but learners sometimes expect an article where Catalan does not use one.

Two reasons:

1. Position: In Catalan, adjectives often come after the noun.

   • guants negres = black gloves

2. Agreement: Adjectives must agree with the noun in gender and number.

   • guant negre = one black glove
   • guants negres = black gloves

Since guants is masculine plural, the adjective must also be masculine plural: negres.

Here a introduces the place where the buying happens: at the shop/store.

Catalan very often uses a with places, especially everyday locations and establishments:

• a casa
• a l'escola
• a la botiga

So a la botiga is a natural way to say at the shop or at the store.

Also:

• a + la stays a la
• unlike a + el, which becomes al

Sometimes learners expect en because English often uses in, but a la botiga is the normal, idiomatic choice here.

In Catalan, a is very commonly used for location with many places. In some contexts or varieties, you may also hear en, but for a sentence like this, a la botiga is the safest and most natural option.

La botiga suggests a specific, identifiable shop, often one already known from context or understood as the usual one.

• a la botiga = at the shop / at the store
• a una botiga = at a shop / at one shop

So the definite article makes it sound more specific.

No. In Catalan, h is silent.

So hivern begins with the vowel sound i, which is also why the article becomes l':

• el hivern → l'hivern

That is pronounced roughly like lee-VERN in Central Catalan-style pronunciation, though exact pronunciation varies by dialect.