Mi madre me prepara té caliente cuando hace frío.

Me is an indirect object pronoun here. It means for me or to me.

So Mi madre me prepara té caliente means something like:

• My mother prepares hot tea for me

In Spanish, this is very natural. Instead of always saying para mí, Spanish often uses an indirect object pronoun:

• Mi madre me prepara té = My mother makes tea for me

You could say Mi madre prepara té para mí, but me prepara sounds more natural in this kind of sentence.

With a normal conjugated verb, object pronouns usually go before the verb in Spanish:

• me prepara
• te ayuda
• nos compra pan

So:

• Mi madre me prepara té caliente is correct.

You would attach the pronoun to the end only in certain cases, such as with:

• infinitives: va a prepararme té
• gerunds: está preparándome té
• affirmative commands: prepárame té

But with prepara as a regular present-tense verb in a statement, me goes before it.

Prepara is the third-person singular present tense form of preparar, because the subject is Mi madre.

• preparar = to prepare
• prepara = she prepares

So:

• Mi madre prepara... = My mother prepares...

Spanish often uses the present tense for habitual actions, just like English:

• Mi madre me prepara té caliente cuando hace frío
  = My mother makes me hot tea when it’s cold

This suggests something she usually does.

Spanish often leaves out the article when talking about something in a general, habitual, or non-specific way.

So:

• me prepara té caliente = she makes me hot tea

This sounds natural when you are talking about the kind of thing she prepares for you in that situation.

If you say:

• me prepara un té caliente

that sounds more like she makes me a hot tea / a cup of hot tea, possibly referring to a more specific instance.

Both can be correct, but the version without un is very natural in a general statement.

In Spanish, adjectives usually come after the noun.

So:

• té caliente = hot tea
• café frío = cold coffee
• pan tostado = toasted bread

This is one of the most basic word-order differences between English and Spanish.

Yes. Adjectives in Spanish usually agree with the noun in gender and number.

Here:

• té is masculine singular
• so the adjective is caliente, which works for masculine singular

In this case, caliente does not change between masculine and feminine singular:

• té caliente
• sopa caliente

But in the plural it would change:

• tés calientes
• sopas calientes

For weather expressions, Spanish often uses hacer:

• hace frío = it’s cold
• hace calor = it’s hot
• hace buen tiempo = the weather is nice

So hace frío is the normal way to say it is cold in the sense of weather.

Es frío usually describes something as being cold by nature or quality, for example:

• El clima aquí es frío = The climate here is cold
• Es una persona fría = He/She is a cold person

But for the weather at a given time, use hace frío.

Cuando means when.

In this sentence, it introduces the situation in which the action happens:

• Mi madre me prepara té caliente cuando hace frío
• My mother makes me hot tea when it’s cold

It shows a habitual relationship:

• when it’s cold, she makes me hot tea

Yes, mi madre is the subject.

Spanish often does not need a subject pronoun like ella, because the verb ending already helps show who is doing the action:

• prepara = she prepares

Since mi madre is already stated, adding ella would usually be unnecessary.

So this is completely natural:

• Mi madre me prepara té caliente

Spanish commonly avoids subject pronouns unless they are needed for emphasis, contrast, or clarity.

Because té with an accent means tea, while te without an accent usually means you as an object pronoun.

Compare:

• té = tea
• te = you

Examples:

• Bebo té = I drink tea
• Te veo = I see you

The accent helps distinguish two words that would otherwise look the same.

Yes. Cuando here can often be understood as when or whenever, depending on context.

Because the whole sentence is in the present tense and describes a usual action, whenever is a very natural English translation:

• My mother makes me hot tea when it’s cold
• My mother makes me hot tea whenever it’s cold

Both work well.

Yes. The Spanish indirect object pronoun me can correspond to several English ideas, including:

• to me
• for me

In this sentence, English most naturally says:

• My mother makes hot tea for me

But grammatically, Spanish just uses the indirect object pronoun me without needing to separate those ideas the way English often does.

Yes, it sounds natural and correct in Spanish from Spain.

It has several very normal features of everyday Spanish:

• Mi madre as the subject
• me prepara with an indirect object pronoun
• té caliente with the adjective after the noun
• cuando hace frío as a standard weather expression

A Spaniard might also say slightly different versions depending on context, such as:

• Mi madre me prepara un té caliente cuando hace frío
• Cuando hace frío, mi madre me prepara té caliente

But your original sentence is perfectly natural.