Quando inizia l’appello, nessuno parla più.

Here quando introduces a time clause: quando inizia l’appello.

It means when in the sense of at the moment that or whenever, depending on context. In this sentence, it most naturally gives a general meaning: this is what happens whenever the roll call begins.

Italian normally uses the indicative after quando when the event is presented as real or factual, which is exactly what is happening here.

Inizia is the present indicative, third person singular, of iniziare.

Italian often uses the present tense for:

• general truths
• habits
• repeated situations

So Quando inizia l’appello, nessuno parla più is like saying: Whenever the roll call begins, nobody talks anymore.

If you were talking about one specific future event, Italian could also use a future form in some contexts, but here the present sounds natural because the sentence describes a regular situation or rule.

Both are possible.

Italian word order is more flexible than English, and with verbs like iniziare it is very common to put the verb before the subject:

• Inizia l’appello
• L’appello inizia

In this sentence, inizia l’appello sounds very natural, especially after an introductory clause like quando. It presents the event almost as it is happening: when the roll call begins.

So this is not unusual or inverted in a strange way; it is a normal Italian pattern.

Because the singular definite article before a vowel is l’.

So:

• il libro
• l’appello
• l’esame

The apostrophe shows elision: the article is shortened before a vowel sound.

Because nessuno is grammatically singular.

Even though it refers to zero people, Italian treats it like no one / nobody, which is singular:

• Nessuno parla
• not Nessuno parlano

So parla is correct because it agrees with nessuno.

Because nessuno is already carrying the negative meaning, and when nessuno comes before the verb, standard Italian usually does not add non.

So this is correct:

• Nessuno parla più

But if nessuno comes after the verb, then non is normally required:

• Non parla più nessuno

Both mean the same thing, but the structure changes.

Here più means any more or any longer, not just more.

In negative sentences, più often has this meaning:

• non parlo più = I don’t speak any more / I no longer speak
• nessuno parla più = no one speaks any more

So in this sentence, più tells you that once the roll call begins, the talking stops.

That is a very natural position for it.

In Italian, adverbs like più often come after the verb:

• non mangio più
• non esce più
• nessuno parla più

Putting più at the end sounds normal and idiomatic here.

The comma is very natural and usually recommended here.

The first part, Quando inizia l’appello, is an introductory subordinate clause. Italian often separates that kind of clause with a comma before the main clause:

• Quando inizia l’appello, nessuno parla più.

In very informal writing, people may sometimes leave the comma out, but with standard punctuation the comma is the better choice.

Yes, with small stylistic differences.

For example:

• Quando l’appello inizia, nessuno parla più.
• Quando inizia l’appello, non parla più nessuno.

These are all possible.

The differences are mostly about rhythm or emphasis, not basic meaning. The original sentence is very natural and well-formed.