Durante l’appello, Marta risponde subito.

Durante means during and is followed by a noun:

• durante l’appello = during roll call

Mentre means while and is usually followed by a clause with a verb:

• Mentre il professore fa l’appello, Marta risponde subito.
  = While the teacher is taking attendance, Marta answers immediately.

So in this sentence, durante is used because l’appello is a noun phrase, not a full clause.

Here l’appello means roll call or attendance-taking, especially in a school context.

So:

• fare l’appello = to call the roll / take attendance

Be careful: appello can also mean appeal in other contexts, but here the classroom context makes roll call the correct meaning.

The base article is lo, because appello begins with a vowel but belongs to the group of masculine nouns that normally take lo before certain consonant sounds in the singular form of the article system. Before a vowel, lo becomes l’:

• lo studente
• lo zaino
• l’appello

So l’appello is simply the correct shortened form before a vowel.

The apostrophe shows elision: the article loses its final vowel before a following vowel.

• lo appello becomes l’appello

This is very common in Italian with articles:

• l’amico
• l’insegnante
• l’idea

Risponde is the third person singular present tense of rispondere (to answer / to respond).

Conjugation:

• io rispondo
• tu rispondi
• lui/lei risponde
• noi rispondiamo
• voi rispondete
• loro rispondono

Since the subject is Marta, which is she, the sentence uses risponde.

Italian often leaves out subject pronouns when the verb ending already makes the subject clear.

So instead of saying:

• Lei risponde subito

Italian very naturally says:

• Marta risponde subito

The name Marta already tells you who the subject is, and risponde matches that subject.

Subito means immediately, right away, or at once. It is an adverb, so it modifies the verb:

• risponde subito = answers immediately

It tells us how quickly Marta answers.

Yes, adverbs in Italian can sometimes move around, though some positions sound more natural than others.

These are possible:

• Marta risponde subito.
• Marta subito risponde.
• Subito, Marta risponde.

The most neutral and natural version here is:

• Marta risponde subito.

That is the version a learner should probably use first.

Sometimes yes, sometimes no.

If you say answer/respond in a general sense, Italian can use rispondere without an expressed object:

• Marta risponde subito.

But if you say what someone is answering to, Italian usually uses a:

• rispondere a una domanda = to answer a question
• rispondere al professore = to answer the teacher
• rispondere al telefono = to answer the phone

In the sentence you gave, the thing being answered is understood from the context of roll call.

It is common and helpful, but not absolutely mandatory in every context.

• Durante l’appello, Marta risponde subito.

The comma separates the introductory time phrase from the main clause. This is very natural in writing.

You may also see:

• Durante l’appello Marta risponde subito.

That is also possible, especially in shorter or less formal writing.

Yes, that is grammatically correct.

• Durante l’appello, Marta risponde subito.
• Marta risponde subito durante l’appello.

Both mean the same basic thing. The difference is mainly one of focus and rhythm:

• Starting with Durante l’appello emphasizes the time/context
• Starting with Marta emphasizes the person

Yes. Risponde is in the present tense.

In Italian, the present tense can describe:

1. What is happening now
2. A habitual action
3. A general fact

So this sentence could mean either:

• During roll call, Marta answers immediately
  as a general habit,

or, depending on context,

• During roll call, Marta is answering immediately

Usually, without extra context, it sounds like a simple present statement or habitual behavior.

Appello is pronounced roughly like ap-PEL-lo.

A few useful points:

• the stress is on -pel-
• the ll is clearly pronounced
• the double consonant after a matters in Italian spelling, though for English speakers the main goal is to keep the word crisp and not overly reduce the vowels

So:

• ap-PEL-lo

And the full phrase:

• Durante l’appello
  roughly: doo-RAN-te lap-PEL-lo

Yes, appello is masculine singular.

That is why it takes the masculine singular article:

• l’appello

Its plural is:

• gli appelli

Though in this classroom meaning, you will most often encounter it in the singular in expressions like:

• fare l’appello
• durante l’appello

Because Italian and English do not always match word for word with prepositions.

Italian uses:

• durante
  • noun = during
    • noun

So:

• Durante l’appello = During roll call

Using in or at would not be the normal way to express this idea in Italian. The sentence is specifically talking about what happens in the course of roll call, so durante is the natural choice.