Quando il significato non è chiaro, la professoressa ci invita a riscrivere la frase con parole più semplici.

Here it is best understood as when/whenever.

Because the sentence uses the present tense in both parts, it describes something that happens regularly or as a general rule:

• Quando il significato non è chiaro... = When/Whenever the meaning is not clear...

So this is not necessarily about one single moment in time; it can mean every time this happens.

Italian uses definite articles very often, including in places where English might sound a bit less article-heavy.

• il significato = the meaning

Here it refers to the meaning of the sentence / of what is being discussed. In Italian, using il sounds completely natural.

In Italian, non normally goes before the conjugated verb.

• è chiaro = it is clear
• non è chiaro = it is not clear

So the standard position is:

• non + verb

The accent distinguishes the verb è from e.

• è = is
• e = and

So in this sentence, è is the verb to be.

Because la professoressa means the teacher/professor, referring to a specific female teacher.

In Italian, common nouns used as subjects usually take an article:

• la professoressa
• il professore
• la studentessa

You would normally omit the article only in direct address:

• Professoressa, posso fare una domanda?

But as the subject of a sentence, la professoressa is correct and natural.

Ci means us.

So:

• la professoressa ci invita = the teacher invites us

It is an unstressed object pronoun, and in Italian these pronouns usually go before the conjugated verb:

• ci invita
• mi invita
• ti invita

Here ci refers to the students.

Because invitare commonly uses this pattern:

• invitare qualcuno a + infinitive

So:

• ci invita a riscrivere = she invites/encourages us to rewrite

Other examples:

• Mi invita a parlare = She invites me to speak
• Li invita a partecipare = She invites them to take part

So the a is required by the verb pattern.

Riscrivere means to rewrite.

It is made up of:

• scrivere = to write
• prefix ri- = again / re-

So:

• riscrivere = write again, usually in the sense of rewrite

In this sentence, it means writing the sentence again in a clearer or simpler way.

La frase means the sentence or sometimes the phrase, depending on context.

Here it most likely means the sentence being worked on.

Again, Italian normally uses the article:

• riscrivere la frase = rewrite the sentence

Saying just riscrivere frase would be incorrect here.

Con here means with in the sense of using:

• con parole più semplici = with simpler words / using simpler words

So the idea is:

• rewrite the sentence using simpler words

This is a very common Italian way to express by using something.

Because the adjective has to agree with parole, which is plural.

• parola = singular
• parole = plural

So:

• una parola più semplice = a simpler word
• parole più semplici = simpler words

Also notice that semplici is the plural form.

Because each adjective agrees with a different noun.

• chiaro agrees with il significato

  • significato is masculine singular
  • so: chiaro

• semplici agrees with parole

  • parole is feminine plural
  • so: semplici

This is a basic but very important rule in Italian: adjectives change to match the noun they describe.

Because the sentence describes a general or habitual situation.

• non è chiaro
• invita
• riscrivere (infinitive, not a finite tense)

The meaning is something like:

• Whenever the meaning is unclear, the teacher asks/encourages us to rewrite the sentence in simpler words.

So the present tense works well because it expresses a repeated classroom practice, not a one-time event.