Al desembre, acostumo a portar guants perquè fa molt fred.

Yes. Al desembre means in December or during December.

Here, al is a contraction of a + el:

• a = to / at / in
• el = the
• al = to the / in the

Catalan often uses the article with months in expressions like this, so al desembre is natural. You may also hear pel desembre in some contexts, but al desembre is very common for in December.

That is a normal difference between English and Catalan.

In Catalan, months often appear with the definite article in time expressions:

• al gener = in January
• al febrer = in February
• al desembre = in December

So even though English does not use the, Catalan often does. You should not translate word-for-word here.

Acostumo a means I usually or I tend to do something.

It comes from the verb acostumar (a), which means to be accustomed to / to usually do.

So:

• acostumo a portar guants = I usually wear gloves
• literally: I am accustomed to wearing gloves

This is a very common way to talk about habits.

Because the verb acostumar normally takes the preposition a before another verb in the infinitive.

Pattern:

• acostumar a + infinitive

Examples:

• Acostumo a llegir abans de dormir. = I usually read before sleeping.
• S’acostumen a llevar d’hora. = They usually get up early.

So acostumo a portar is the correct structure.

Yes, absolutely.

These are both natural:

• Acostumo a portar guants = I usually wear gloves / I tend to wear gloves
• Normalment porto guants = I normally wear gloves

The difference is small:

• acostumo a emphasizes habit
• normalment is a simple adverb meaning normally / usually

Both work well in this sentence.

Yes. In Catalan, portar can mean to wear when talking about clothes or accessories.

So:

• portar guants = to wear gloves
• portar un barret = to wear a hat
• portar ulleres = to wear glasses

Depending on the region, you may also hear dur with the same meaning:

• dur guants = to wear gloves

But portar is completely standard and very common.

Because Catalan often omits the article when speaking generally about clothing or plural countable items after verbs like portar.

So:

• portar guants = to wear gloves
• portar sabates = to wear shoes

If you say els guants, it sounds more like you mean specific gloves:

• Porto els guants que em vas regalar. = I’m wearing the gloves you gave me.

In your sentence, the meaning is general, so guants without an article is the natural choice.

Here perquè means because.

The accent matters. In Catalan:

• perquè = because
• per què = why / for what reason
• per a què or sometimes per què in some contexts = what for / so that

So in this sentence:

• ... perquè fa molt fred = ... because it is very cold

The accent helps distinguish it from other similar forms.

This is a fixed Catalan weather expression.

Fer is used in many expressions about weather:

• fa fred = it is cold
• fa calor = it is hot
• fa vent = it is windy
• fa sol = it is sunny

So fa molt fred simply means it is very cold.

Even if it sounds strange from an English perspective, this is the normal Catalan way to express this idea.

Because fred here works as a noun in a weather expression, and molt directly modifies it.

So:

• fa molt fred = it is very cold
• fa massa fred = it is too cold

You do not normally say fa molt de fred in standard usage for this basic weather statement. The usual form is fa molt fred.

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

• acostumo already means I usually
• so jo is not necessary

You could say:

• Jo acostumo a portar guants...

But that would add emphasis, contrast, or clarity. In ordinary sentences, Catalan usually leaves the pronoun out.

It is very natural, because Al desembre is an introductory time expression.

So this punctuation is good:

• Al desembre, acostumo a portar guants perquè fa molt fred.

The comma helps separate the time phrase from the main clause. In less formal writing, some people might omit it, but using it here is a good choice.

Very roughly, it is:

• Al desembre = In December
• acostumo a portar = I usually wear / I tend to wear
• guants = gloves
• perquè = because
• fa molt fred = it is very cold

So a word-for-word style gloss would be something like:

In December, I-usually-to wear gloves because it-makes a-lot cold.

That is not good English, of course, but it can help you see how the Catalan sentence is built.

A simple learner-friendly guide:

• perquè sounds roughly like per-KEH
• guants sounds roughly like GWANTS

A few tips:

• In perquè, the stress is on the last part: -què
• In guants, the gua- starts like gwa-
• The final -ts is pronounced

So the full sentence is approximately:

Al de-sem-bre, a-cos-TU-mo a por-TAR GWANTS per-KEH fa molt fret.

This is only an approximation, but it is a useful starting point.