Learn Hardcore Portuguese (Brazil): A autora é muito inteligente.

A autora é muito inteligente. = The (specific) author is very intelligent.
Uma autora é muito inteligente. = An author is very intelligent. (non‑specific; this is less usual in this context)

Also note the difference:

Ela é autora. = She is an author. (no article after ser when stating profession in general)
Ela é a autora. = She is the author. (a specific one that we have in mind)

Why autora and not autor? What is the difference?

Autora is the feminine form of autor.

autor = author (male)
autora = author (female)

Many Portuguese nouns for jobs or roles change ending from -or (masculine) to -ora (feminine):

doutor / doutora – doctor
professor / professora – teacher
ator / atriz (irregular) – actor / actress

So A autora é muito inteligente clearly tells you the author is female.

How would the sentence change if the author were male?

You change both the article and the noun to the masculine form:

O autor é muito inteligente. = The (male) author is very intelligent.

For plural forms:

As autoras são muito inteligentes. = The female authors are very intelligent.
Os autores são muito inteligentes. = The male (or mixed‑gender) authors are very intelligent.

Why is it é and not está? What is the difference between ser and estar here?

É is from ser; está is from estar. Both translate as is, but they are used differently.

ser (é) is used for essential, more permanent characteristics:
- A autora é muito inteligente.
  You are describing an inherent quality: she is a smart person in general.
estar (está) is used for temporary states or conditions:
- A autora está cansada. = The author is tired (right now).
- A autora está nervosa hoje. = The author is nervous today.

Intelligence is seen as a stable trait, so you use é, not está.

What exactly does muito mean here, and where should it go in the sentence?

In this sentence, muito means very. It is an adverb of intensity modifying the adjective inteligente.

inteligente = intelligent
muito inteligente = very intelligent

Placement: muito normally goes before the adjective or adverb it modifies:

muito inteligente – very intelligent
muito alto – very tall
muito bem – very well

So the normal order is:

A autora é muito inteligente.
(subject) (verb) (adverb) (adjective)

You cannot put it after the adjective in this case:

A autora é inteligente muito ❌ (incorrect)

Why is it muito inteligente and not muita inteligente? Doesn’t muito change with gender?

Muito does two different jobs in Portuguese:

Adjective meaning much / many – it changes with gender and number:
- muito dinheiro – much money
- muita água – much water
- muitos livros – many books
- muitas pessoas – many people
Adverb meaning very / a lot – it is invariable (it does not change):
- muito inteligente – very intelligent
- muito feliz – very happy
- gosta muito – likes it a lot

In A autora é muito inteligente, muito is an adverb modifying inteligente, so it stays muito, regardless of feminine or masculine:

A autora é muito inteligente.
O autor é muito inteligente.

Never muita inteligente.

Why is the adjective inteligente the same for masculine and feminine? Why not inteligento or inteligenta?

In Portuguese, many adjectives have two gender forms (masculine and feminine):

bonito / bonita – pretty
cansado / cansada – tired

But adjectives that end in -e or -z are usually the same for masculine and feminine. They only change in the plural:

inteligente (singular, masc/fem) → inteligentes (plural, masc/fem)
feliz (singular, masc/fem) → felizes (plural, masc/fem)

So:

A autora é inteligente. – The female author is intelligent.
O autor é inteligente. – The male author is intelligent.

There is no form inteligento or inteligenta in standard Portuguese.

Can I leave out muito? What is the difference in meaning?

Yes, you can leave it out.

A autora é inteligente. = The author is intelligent.
A autora é muito inteligente. = The author is very intelligent.

Adding muito strengthens the adjective.
Without muito, you just state the quality; with muito, you emphasize its degree.

How do I make this sentence negative? How do I say “The author is not very intelligent”?

To make a sentence negative in Portuguese, you normally put não before the verb.

A autora é muito inteligente.
A autora não é muito inteligente. = The author is not very intelligent.

Pattern:
[subject] + não + [verb] + [rest of sentence]

You cannot put não at the end like in English “… is very intelligent not”.

How do I pronounce A autora é muito inteligente?

Approximate Brazilian Portuguese pronunciation (using English-like hints):

A – like “ah”
autora – aw-TOH-rah
- au like “ow” in “cow” but quicker
- stress on TO: au-TO-ra
é – like “eh” in “bet”, but a bit more open
muito – MOOY-toh
- in most Brazilian accents, it sounds like “MOOY-too” with a quick y glide
- nasalized mũi sound: lips don’t fully close as for an English m
inteligente – roughly een-teh-leh-ZHEN-chee
- in similar to “een”
- te like “teh”
- ge = “zh” as in “vision”
- final -te often sounds like “chee” in Brazilian Portuguese
- stress on GEN: in-te-le-GEN-te

Full sentence (Brazilian Portuguese, roughly):
[ah aw-TOH-rah eh MOOY-toh een-teh-leh-ZHEN-chee]

If you know IPA:
[a awˈtoɾa ɛ ˈmũj.tu ĩ̃teleˈʒẽ.tʃi] (pronunciation varies a bit by region).