En verano, empiezo a sudar si camino muy rápido hasta la estación.

In Spanish, seasons are often used without the article after en:

• en verano = in summer
• en invierno = in winter

So En verano is the most natural general way to say in summer.

You may sometimes hear en el verano, but it usually sounds more specific or regional. For a broad general statement like this one, en verano is the standard choice.

Spanish often drops subject pronouns because the verb ending already shows who is doing the action.

• empiezo = I begin / I start

So yo is not necessary. You could say Yo empiezo a sudar... if you want extra emphasis, but normally Spanish prefers just empiezo.

Both are possible, but they mean slightly different things.

• sudo = I sweat
• empiezo a sudar = I start to sweat / I begin sweating

The sentence uses empiezo a sudar to highlight the moment the sweating begins, not just the general action.

So:

• En verano, sudo si camino muy rápido... = In summer, I sweat if I walk very fast...
• En verano, empiezo a sudar si camino muy rápido... = In summer, I start to sweat if I walk very fast...

The second version feels a bit more vivid and specific.

Because empezar is followed by a + infinitive when it means to start doing something.

Pattern:

• empezar a + infinitive

Examples:

• empiezo a sudar = I start to sweat
• empieza a llover = it starts to rain
• empezamos a comer = we start eating

You cannot say empiezo sudar.

Because empezar is a stem-changing verb in the present tense.

The e in the stem changes to ie in some forms:

• yo empiezo
• tú empiezas
• él/ella empieza
• nosotros empezamos
• vosotros empezáis
• ellos/ellas empiezan

So empiezo is the correct yo form.

Because this is a real or likely condition, so Spanish uses si + present indicative.

• si camino muy rápido = if I walk very fast

This is talking about something that really can happen, so the indicative is correct.

A very common pattern is:

• si + present, present
• si + present, future
• si + imperfect subjunctive, conditional

Here, the speaker means: whenever this happens, this is the result.

Both caminar and andar can mean to walk, but caminar is often the clearer, more neutral choice when talking about walking somewhere.

• caminar = to walk
• andar = to walk, to go around, to move about

In this sentence, camino muy rápido hasta la estación sounds straightforward and natural: if I walk very fast to the station.

If you said ando muy rápido, it might also work in some contexts, but caminar is often a better match for purposeful walking to a destination.

Because muy is used before adjectives and adverbs, while mucho usually refers to quantity.

Here rápido is working adverbially, describing how you walk:

• camino muy rápido = I walk very fast

Compare:

• muy rápido = very fast
• mucho = a lot

So you could say:

• camino muy rápido = I walk very fast
• camino mucho = I walk a lot

But not mucho rápido.

Here it functions like an adverb, even though the form is the same as the adjective.

• rápido as an adjective: un tren rápido = a fast train
• rápido used adverbially: camino rápido = I walk fast

Spanish often uses the masculine singular adjective form adverbially in everyday speech. You may also hear rápidamente, which is the more explicitly adverbial form:

• camino muy rápido
• camino muy rápidamente

Both are correct, but muy rápido is usually more natural in everyday conversation.

Here hasta la estación means as far as the station or more naturally to the station.

With movement verbs, hasta can mark the end point of the movement:

• camino hasta la estación = I walk to the station

It suggests the station is the point you reach.

In many cases, caminar a la estación is also possible, but hasta la estación strongly marks the destination as the endpoint of the walk.

Yes, estación can mean both:

• station
• season

But context makes the meaning clear.

In this sentence:

• En verano already expresses in summer
• hasta la estación must mean to the station

So there is no real confusion here.

Yes. Spanish word order is fairly flexible, especially with time phrases and si clauses.

For example, these are all possible:

• En verano, empiezo a sudar si camino muy rápido hasta la estación.
• Si camino muy rápido hasta la estación, empiezo a sudar en verano.
• Empiezo a sudar si camino muy rápido hasta la estación en verano.

But the original sentence sounds natural because it starts with the general time setting En verano.

It is very natural and helpful, because En verano is an introductory time phrase.

• En verano, empiezo a sudar...

In short sentences, Spanish sometimes omits this comma, but including it makes the structure clearer and is a good choice in writing.

It most naturally describes a general habit or repeated situation.

That is because it uses the present tense with a conditional idea:

• empiezo
• camino

So the meaning is something like:

• In summer, I start to sweat if I walk very fast to the station.

This sounds like something that generally happens whenever those conditions are true, not one single event.