Prima di stampare il documento, devi selezionare la pagina giusta.

Because prima di is the normal way to say before when it is followed by a verb in the infinitive.

• prima di stampare = before printing / before you print
• prima di uscire = before leaving
• prima di mangiare = before eating

So in this sentence, prima di stampare il documento means before printing the document.

If Italian uses a full clause with a different subject, it often switches to prima che + subjunctive:

• Prima di stampare il documento, devi... = before printing the document...
• Prima che tu stampi il documento, devi... = before you print the document...

It is in the infinitive because it comes after prima di.

This is very common in Italian:

• prima di partire
• prima di leggere
• prima di selezionare

English often uses either:

• before printing
• before you print

Italian does not use a gerund here in the same way English does. It simply uses prima di + infinitive.

Devi is the second person singular of dovere, meaning to have to / must.

So:

• devo = I must / I have to
• devi = you must / you have to
• deve = he/she/it must

Here, devi selezionare means:

• you must select
• you have to select

It gives an instruction or requirement.

Italian often drops subject pronouns because the verb ending already shows who the subject is.

• devi already tells us the subject is you singular
• so (tu) devi is possible, but tu is often omitted

Compare:

• Devi selezionare la pagina giusta. = You have to select the right page.
• Tu devi selezionare la pagina giusta. = You have to select the right page.

Adding tu gives extra emphasis, contrast, or clarity, but it is not necessary.

Italian nouns usually have grammatical gender, and the article must match.

• documento is masculine singular, so it takes il
• pagina is feminine singular, so it takes la

So:

• il documento = the document
• la pagina = the page

This is something you usually learn together with the noun:

• il libro
• la casa
• il documento
• la pagina

Even if a noun refers to an object, it still has grammatical gender.

In Italian, adjectives often come after the noun.

So:

• la pagina giusta = the right/correct page
• il documento importante = the important document

This noun + adjective order is very common.

With giusto, putting it after the noun usually means correct/right in the practical sense:

• la risposta giusta = the correct answer
• la pagina giusta = the correct page

If the adjective comes before the noun, the meaning can sometimes shift or sound more literary or emphatic, but here la pagina giusta is the normal choice.

Here, giusta means right in the sense of correct.

So la pagina giusta means:

• the right page
• the correct page

It does not mean just/fair in this sentence.

The adjective giusto/giusta can have different meanings depending on context:

• la risposta giusta = the correct answer
• una decisione giusta = a fair/just decision
• giusto! = exactly! / that’s right!

Here the context is printing, so the meaning is clearly correct.

The comma separates the introductory phrase from the main clause:

• Prima di stampare il documento, = introductory time phrase
• devi selezionare la pagina giusta. = main clause

In English, you would often write the same kind of comma:

• Before printing the document, you must select the correct page.

In Italian, the comma is very natural here, especially because the opening phrase is fairly long.

Yes, absolutely.

Both are correct:

• Prima di stampare il documento, devi selezionare la pagina giusta.
• Devi selezionare la pagina giusta prima di stampare il documento.

The difference is mostly about emphasis and flow.

• Starting with Prima di stampare il documento emphasizes the time/order first.
• Starting with Devi selezionare la pagina giusta emphasizes the instruction first.

Both mean the same thing.

You could sometimes use scegliere, but selezionare is more natural in a technical or computer-related context.

• selezionare = to select
• scegliere = to choose

When talking about software, printers, menus, settings, or options, selezionare is often the best match for English select:

• selezionare una pagina
• selezionare un file
• selezionare un’opzione

Scegliere is broader and often used for making a choice:

• scegliere un vestito = choose an outfit
• scegliere un ristorante = choose a restaurant

In this sentence, selezionare sounds more precise and idiomatic.

Because the sentence is talking about selecting the correct page, meaning one specific page.

• la pagina giusta = the correct page
• le pagine giuste = the correct pages

If you needed more than one page, Italian would use the plural:

• devi selezionare le pagine giuste

But here the sentence is referring to one page only.

In everyday modern Italian, yes, stampare is the normal verb for to print, especially for documents, pages, emails, and files.

Examples:

• stampare un documento = to print a document
• stampare una foto = to print a photo
• stampare una pagina = to print a page

It can also mean to print in a publishing sense:

• stampare un libro = to print a book

So this is a very useful and common verb.

Yes. That is one reason this structure is so common.

Italian prima di + infinitive can often correspond to either:

• before printing the document
• before you print the document

English has two natural ways to express it, but Italian uses the infinitive very comfortably here as long as the subject is understood from context.

So the Italian phrase is slightly more compact than one possible English translation, but the meaning is the same.