A diretora escreveu com giz no quadro e depois apagou tudo.

Because diretora is a feminine noun, so it takes the feminine article a.

• o diretor = the male director/principal
• a diretora = the female director/principal

In Portuguese, articles usually agree in gender and number with the noun.

In this sentence, diretora most likely means principal or director, depending on context.

In Brazilian Portuguese, diretor/diretora can be used for:

• a school principal
• a director of a company or institution
• a film or theater director

Because the sentence mentions giz and quadro, a school setting is the most natural interpretation.

They are both in the preterite, which is the tense commonly used in Brazilian Portuguese for completed past actions.

• escrever → escreveu = wrote
• apagar → apagou = erased

Both forms are third person singular, matching a diretora.

So the sentence describes two completed actions:

1. she wrote
2. then she erased everything

Because the verbs belong to different conjugation groups.

• escrever is an -er verb, so in the preterite, ele/ela/você becomes escreveu
• apagar is an -ar verb, so in the preterite, ele/ela/você becomes apagou

This is a very common pattern:

• falar → falou
• comer → comeu
• abrir → abriu

Com means with, and here it shows the instrument used to write.

So escreveu com giz means she wrote using chalk.

Portuguese often uses com for tools or instruments:

• escrever com caneta = to write with a pen
• cortar com faca = to cut with a knife
• pintar com pincel = to paint with a brush

Also, giz appears without an article because it is being used in a general sense: chalk as a material/tool, not a specific piece of chalk.

Because no is the contraction of em + o.

• em o → no
• em a → na
• em os → nos
• em as → nas

So:

• no quadro = on the board / in the board depending on context, but here naturally on the board

These contractions are required in normal Portuguese.

Yes, quadro can mean several things, and context tells you which one is meant.

Common meanings of quadro include:

• picture/painting
• frame
• panel/chart
• board

In a classroom context, especially with giz, quadro clearly means a writing board, like a blackboard or chalkboard.

In Brazil, people may also say:

• quadro-negro = blackboard
• lousa = board
• quadro branco = whiteboard

Depois means afterward, then, or later. It links the two actions in sequence.

Here, e depois apagou tudo means something like and then erased everything.

Its position is flexible. For example:

• A diretora escreveu com giz no quadro e depois apagou tudo.
• A diretora escreveu com giz no quadro e apagou tudo depois.
• Depois, a diretora apagou tudo.

All of these are possible, though the original version sounds very natural.

Here, tudo means everything.

• apagou tudo = erased everything

This is different from todo, which usually works like all or whole and normally comes with a noun or changes form to agree with one.

Compare:

• apagou tudo = erased everything
• apagou todo o texto = erased all the text
• apagou toda a frase = erased the whole sentence

So tudo stands alone, while todo/toda/todos/todas usually goes with a noun.

Yes, but it is not exactly the same.

• apagou tudo focuses on what was written: she erased everything
• apagou o quadro focuses more on the board itself: she erased/cleaned the board

In many situations they can overlap, but apagou tudo is more precise if you want to say all the writing disappeared.

Because Portuguese often omits subject pronouns when the subject is already clear.

The sentence already has A diretora, so adding ela would be unnecessary:

• A diretora escreveu... = perfectly natural
• Ela escreveu... = also possible if the person is already known from context

Portuguese does this much more often than English.

In Brazilian Portuguese, giz is pronounced approximately like zhees, with these details:

• g before i sounds like the s in measure or the zh sound
• the vowel is like ee
• final z in this word is pronounced like s

So giz sounds roughly like zhees.

A few other useful pronunciations from the sentence:

• diretora ≈ jee-reh-TOH-rah
• quadro ≈ KWA-droo
• escreveu ≈ es-kreh-VEH-oo
• apagou ≈ ah-pah-GOH

These are only rough English approximations, but they can help at first.

Yes, it is completely natural.

The structure is very straightforward:

• A diretora = subject
• escreveu = first verb
• com giz = instrument
• no quadro = location
• e depois = sequence connector
• apagou tudo = second action + object

It sounds like normal everyday Portuguese and is exactly the kind of sentence a Brazilian speaker might say.