Per arrivare al mercato, devi svoltare a sinistra dopo il semaforo.

In this sentence, per + infinitive means in order to do something.

So:

• per arrivare al mercato = to get to the market / in order to arrive at the market

This is a very common Italian structure:

• Per capire, devi ascoltare bene. = To understand, you have to listen carefully.
• Per entrare, serve un biglietto. = To enter, you need a ticket.

English often just uses to, but Italian often uses per + infinitive when expressing purpose.

Because a + il contracts to al in Italian.

So:

• a + il = al
• arrivare al mercato = arrive at the market

This kind of contraction is very common:

• a + la = alla
• a + i = ai
• a + gli = agli
• a + le = alle

Examples:

• Vado al cinema.
• Parlo alla ragazza.
• Andiamo ai negozi.

With arrivare, Italian often uses a before a specific destination.

So:

• arrivare al mercato
• arrivare alla stazione
• arrivare al ristorante

This is different from some other cases, such as:

• arrivare in Italia
• arrivare in città

A simple way to think about it is:

• a is often used before a specific place
• in is often used with countries, regions, or some broader places

Devi is the second person singular form of dovere, which means to have to or must.

So:

• io devo = I have to
• tu devi = you have to
• lui/lei deve = he/she has to

In this sentence:

• devi svoltare = you have to turn

Depending on context, devi can sound like:

• you have to
• you need to
• sometimes even you must

In directions, it usually sounds practical rather than forceful.

Not necessarily. In directions, devi is very natural and often just means you need to.

But yes, Italian can sound softer in other ways, for example:

• Per arrivare al mercato, puoi svoltare a sinistra... = To get to the market, you can turn left...
• Per arrivare al mercato, bisogna svoltare a sinistra... = To get to the market, one has to turn left...
• Per arrivare al mercato, basta svoltare a sinistra... = To get to the market, you just need to turn left...

So devi is normal, but it is not the only option.

Because a sinistra is a fixed expression in Italian, just like a destra.

So:

• svoltare a sinistra = turn left
• svoltare a destra = turn right

You generally do not say just svoltare sinistra.

Other similar expressions include:

• andare a sinistra
• tenere la sinistra = keep left

This is simply the standard Italian pattern.

Yes, you often can.

Both svoltare and girare can be used for turning in directions:

• svoltare a sinistra
• girare a sinistra

In many everyday situations, both sound natural. However:

• svoltare is especially common in road and route directions
• girare is more general and can mean turn in many senses

For example:

• Gira la chiave. = Turn the key.
• Svolta alla prossima strada. = Turn at the next street.

So in this sentence, svoltare is a very natural choice for giving directions.

It usually means after the traffic light, meaning once you pass it, the turn comes after it.

So the sequence is:

1. you reach the traffic light
2. you go past it
3. then you turn left

It does not normally mean before the traffic light.

If someone wanted to say before the traffic light, they would say:

• prima del semaforo

In normal everyday Italian, semaforo usually means traffic light.

So:

• dopo il semaforo = after the traffic light

It is a masculine noun:

• il semaforo
• i semafori

Examples:

• C’è un semaforo davanti alla scuola.
• Aspetta al semaforo.

The comma separates the introductory phrase from the main clause:

• Per arrivare al mercato, = introductory purpose phrase
• devi svoltare a sinistra dopo il semaforo. = main clause

In writing, this comma is very natural and helps readability. In shorter sentences, punctuation can sometimes vary, but here the comma is perfectly standard.

Yes, and it would still be natural.

The difference is small:

• Per arrivare al mercato focuses on reaching the destination
• Per andare al mercato focuses more generally on going there

In directions, both can work:

• Per arrivare al mercato, devi svoltare...
• Per andare al mercato, devi svoltare...

The version with arrivare can sound a little more precise when giving route instructions.

Yes. You could say:

• Per arrivare al mercato, tu devi svoltare a sinistra dopo il semaforo.

But in Italian, subject pronouns are often omitted because the verb already shows the person:

• devi already tells us it means you have to

So normally, the sentence is more natural without tu unless you want emphasis or contrast.

For example:

• Io vado dritto, ma tu devi svoltare a sinistra.

The sentence can be rearranged in a few ways without changing the basic meaning.

For example:

• Devi svoltare a sinistra dopo il semaforo per arrivare al mercato.
• Dopo il semaforo, devi svoltare a sinistra per arrivare al mercato.

These are all natural. The original version starts with the purpose:

• Per arrivare al mercato...

That is a very common and clear way to introduce directions.