Per arrivare in orario, devi camminare più in fretta.

Because per + infinitive is a very common Italian structure meaning to or in order to do something.

So:

• per arrivare = to arrive / in order to arrive

After per in this kind of purpose expression, Italian normally uses the infinitive if the subject is the same as in the main clause.

In this sentence, the person who must walk faster is also the person who wants to arrive on time, so per arrivare is the natural choice.

Examples:

• Per capire, devi ascoltare bene. = To understand, you have to listen carefully.
• Per entrare, devi aprire la porta. = To get in, you have to open the door.

Per arrivi would not work here.

Here per means to or in order to.

Italian per has several meanings depending on context, including:

• for
• to
• in order to
• sometimes through/by

In this sentence, it introduces the goal or purpose:

• Per arrivare in orario... = To arrive on time...

So this is not the for of possession or benefit, but the for the purpose of idea.

Because Italian often leaves out subject pronouns when they are clear from the verb form.

• devi already means you must / you have to
• so tu is unnecessary unless you want emphasis or contrast

Compare:

• Devi camminare più in fretta. = You have to walk faster.
• Tu devi camminare più in fretta. = You have to walk faster.
  This sounds more emphatic, as if contrasting with someone else.

This is one of the big differences from English: Italian usually does not need to state the subject pronoun.

Devi is the second person singular of dovere.

Present tense of dovere:

• io devo
• tu devi
• lui/lei deve
• noi dobbiamo
• voi dovete
• loro devono

Dovere usually means:

• must
• have to
• sometimes should, depending on context

In this sentence:

• devi camminare = you have to walk

It is followed by another verb in the infinitive, which is very common with modal verbs in Italian.

Because after modal verbs such as dovere, potere, and volere, the next verb normally stays in the infinitive.

So:

• devi camminare = you have to walk
• puoi entrare = you can enter
• voglio mangiare = I want to eat

This works much like English:

• must walk
• can enter
• want to eat

So devi camminare is the normal structure: conjugated modal verb + infinitive.

Yes, in orario is a common expression meaning on time or on schedule.

In this sentence:

• arrivare in orario = to arrive on time

It is very natural Italian.

You may also see:

• essere in orario = to be on time
• arrivare puntuale = to arrive on time / punctually

A useful distinction:

• in orario often suggests being on schedule
• puntuale often emphasizes punctuality

In many everyday contexts, though, they are quite close in meaning.

Più in fretta means faster or more literally more quickly / in more haste.

Breakdown:

• più = more
• in fretta = quickly / in a hurry

Together:

• camminare più in fretta = to walk faster

This is functioning adverbially: it tells you how you have to walk.

So Italian is not saying a faster walk here; it is saying you must walk in a faster way.

Because in fretta is the standard expression.

The noun fretta means hurry, but when Italian wants to express the adverbial idea quickly / in a hurry, it commonly uses the fixed phrase:

• in fretta

Examples:

• Sbrigati, siamo in fretta. = Hurry up, we’re in a rush.
• Mangia in fretta. = Eat quickly.
• Cammina più in fretta. = Walk faster.

So the preposition in is part of the idiomatic expression.

Yes. Più velocemente is grammatically correct and means essentially the same thing: more quickly / faster.

So you could say:

• Devi camminare più velocemente.

However, più in fretta is often more common and conversational in everyday speech.

A rough comparison:

• più in fretta = very natural, common, everyday
• più velocemente = also correct, slightly more formal or more explicitly adverbial

Both are good Italian.

Because veloce is usually an adjective, while here you need something that modifies the verb camminare.

You are describing how someone walks, so Italian normally uses an adverbial expression:

• più in fretta
• più velocemente

You may hear things like:

• cammina veloce

in spoken Italian, and it is common in informal usage. But in a sentence like this, più in fretta is more standard and natural for learners to model.

So:

• camminare più in fretta = best natural option here
• camminare più velocemente = also correct
• camminare più veloce = heard in speech, but less standard in careful grammar

The given word order is the most natural:

• Per arrivare in orario, devi camminare più in fretta.

Italian does allow some flexibility, but not every rearrangement sounds natural.

For example, this is still possible:

• Devi camminare più in fretta per arrivare in orario.

This puts the purpose phrase at the end instead of the beginning.

But something like:

• devi camminare in fretta più

is wrong.

So while the sentence can sometimes be reordered for emphasis, più in fretta should stay together as a unit.

Yes, slightly.

• arrivare in orario = to arrive on time
• essere in orario = to be on time / to be on schedule

The first focuses on the moment of arrival. The second focuses on one’s state or overall timing.

Examples:

• Se parti adesso, arrivi in orario. = If you leave now, you’ll arrive on time.
• Siamo in orario. = We’re on time.

In your sentence, arrivare in orario is the right choice because the goal is reaching a place on time.

Yes, depending on context, devi can sometimes sound like you should in natural English, even though its core meaning is stronger: you must / you have to.

For example:

• If a friend is giving practical advice, English might naturally say you should walk faster.
• But the Italian still uses devi because it expresses necessity from the situation.

So the exact English wording can shift:

• you have to walk faster
• you need to walk faster
• sometimes you should walk faster

Grammatically, though, devi is the verb of necessity.

Yes. Devi is singular, so it is addressing one person informally: you = tu.

If you were speaking to several people, you would say:

• Per arrivare in orario, dovete camminare più in fretta.

If you wanted the formal singular you, Italian would normally use:

• Per arrivare in orario, deve camminare più in fretta.

So the verb form tells you who is being addressed.