A professora disse que a ortografia da última palavra está errada.

In Portuguese, it is very common to use the definite article before a noun, even when English would not.

So A professora literally looks like the teacher, but in context it can simply mean the teacher in a normal, natural way, not necessarily with extra emphasis.

Also, professora is feminine, so the article is a.
If the teacher were male, it would be O professor.

Portuguese nouns often show gender. A female teacher is professora, and a male teacher is professor.

The article changes too:

• a professora = the female teacher
• o professor = the male teacher

This grammatical gender also affects adjectives later in the sentence.

Disse is the pretérito perfeito of dizer = to say / to tell.

Here it means said:

• A professora disse = The teacher said

This tense is used for a completed action in the past.

A few forms of dizer are:

• eu digo = I say
• ela diz = she says
• ela disse = she said

So disse is an irregular past form that you simply need to learn.

Here que means that and introduces a subordinate clause.

• A professora disse que... = The teacher said that...

Just like in English, that can sometimes be omitted in translation, but in Portuguese que is normally kept in this structure.

So the sentence is built like this:

• A professora disse = the teacher said
• que a ortografia da última palavra está errada = that the spelling of the last word is wrong

Ortografia is a feminine noun in Portuguese, so it takes the feminine article a.

• a ortografia = the spelling / orthography

Portuguese usually uses articles more often than English does, so where English might say spelling, Portuguese often says a ortografia.

Because de + a contracts into da.

So:

• de = of
• a = the
• da = of the

Therefore:

• a ortografia da última palavra = the spelling of the last word

Other common contractions are:

• do = de + o
• na = em + a
• no = em + o

These contractions are a very important part of natural Portuguese.

In Portuguese, adjectives usually come after the noun, but some very common adjectives can come before it, especially words like último, primeiro, bom, etc.

So:

• a última palavra = the last word

Also, the adjective has to agree with the noun:

• palavra is feminine singular
• so the adjective becomes última, also feminine singular

Compare:

• o último livro = the last book
• a última palavra = the last word

This is about estar vs. ser.

Portuguese often uses estar for a condition or state, including something being incorrect in a specific case.

• está errada = is wrong / is incorrect

Here the teacher is saying that the spelling of that word is wrong. That is treated as a current state of that spelling.

Using é errada would sound different and less natural here. It could suggest a more general or defining characteristic, which is not what this sentence wants.

So in this context, está errada is the natural choice.

Because errada agrees with ortografia, not with palavra.

The subject of the second clause is:

• a ortografia = the spelling

Since ortografia is feminine singular, the adjective must also be feminine singular:

• errada

So the structure is:

• A ortografia ... está errada
• The spelling ... is wrong

Even though palavra is also feminine, the key point is that errada describes ortografia.

Both can be related to spelling, but they are not always used in exactly the same way.

• ortografia often refers to spelling correctness or spelling as a system
• grafia often refers more to the written form of a specific word

In real life, a Brazilian speaker might also say:

• A grafia da última palavra está errada.

That would also be natural.
But ortografia works well here, especially if the focus is on spelling being incorrect.

The sentence follows a very normal Portuguese pattern:

• A professora = subject
• disse = verb
• que... = introduces the reported statement

Then inside the second clause:

• a ortografia da última palavra = subject
• está = verb
• errada = adjective/complement

So the structure is:

Subject + verb + que + subject + verb + adjective

That makes the whole sentence quite straightforward grammatically, even though it contains a subordinate clause.

A rough pronunciation guide for Brazilian Portuguese would be something like:

a pro-fe-SO-ra JEE-see ki a or-to-gra-FI-a da OOL-ti-ma pa-LA-vra es-TA e-HA-da

A few helpful notes:

• disse sounds roughly like JEE-see in many Brazilian accents
• que here sounds like ki
• última has stress on the first syllable: OOL
• está has stress on the last syllable: ta
• rr in errada is a strong Brazilian h-like sound in many accents

This is only an approximation, but it can help you recognize the sentence when you hear it.

Usually disse is best translated here as said.

• A professora disse que... = The teacher said that...

If you want told, Portuguese often uses disse a alguém or sometimes falou para alguém, depending on the structure.

For example:

• A professora me disse que... = The teacher told me that...

So in your sentence, since no listener is mentioned, said is the most natural translation.