A estrada parece perigosa.

Because estrada is a feminine noun in Portuguese. Singular definite articles must match the noun’s gender:

• a estrada = the road
• o caminho = the path

This grammatical gender is something you usually just have to learn with each noun.

Because adjectives usually agree with the noun they describe in gender and number.

Here, estrada is feminine singular, so the adjective must also be feminine singular:

• estrada perigosa = dangerous road
• caminho perigoso = dangerous path
• estradas perigosas = dangerous roads

So perigosa matches a estrada.

Parece is from the verb parecer, which means to seem or to appear.

So A estrada parece perigosa suggests an impression or observation, not a firm statement of fact. It is closer to:

• The road seems dangerous
• The road looks dangerous

It is softer and less direct than saying the road definitely is dangerous.

Because the subject is a estrada, which is singular.

The verb must agree with the subject:

• A estrada parece perigosa. = The road seems dangerous.
• As estradas parecem perigosas. = The roads seem dangerous.

So parece is the correct third-person singular form.

Yes, but the meaning changes a little.

• A estrada parece perigosa. = The road seems dangerous.
• A estrada está perigosa. = The road is dangerous right now / is in a dangerous condition.
• A estrada é perigosa. = The road is dangerous in a more general or inherent sense.

So parece is about appearance or impression, while está and é sound more definite.

In normal Portuguese, yes, a estrada sounds most natural.

Portuguese uses definite articles more often than English does. Leaving it out can sound unnatural in ordinary speech unless you are speaking very generally, writing a headline, or using a special style.

Compare:

• A estrada parece perigosa. = natural, standard sentence
• Estrada parece perigosa. = unusual in normal conversation

Not exactly.

• estrada = road, often between places, outside city centers, or a larger route
• rua = street, usually in a town or city
• rodovia = highway
• caminho = path / way / track

So estrada is the right word if you mean a road rather than a city street.

A simple approximation is:

ah es-TRAH-dah pah-REH-see peh-ree-GOH-zah

A few useful pronunciation notes:

• estrada has the stress on tra
• parece has the stress on re
• perigosa has the stress on go
• The s in perigosa sounds like z because it is between vowels
• The final unstressed e in parece often sounds like ee in Brazilian Portuguese

A more natural Brazilian pronunciation is roughly:

a es-TRA-da pa-RE-si pe-ri-GO-za

Yes. Parecer is often translated as to seem, but in many contexts to look also works well in English.

For example:

• A estrada parece perigosa. = The road seems dangerous. / The road looks dangerous.
• Ela parece cansada. = She seems tired. / She looks tired.

So the best English choice depends on the context.

The standard, natural order is:

A estrada parece perigosa.

That is:

• subject: a estrada
• verb: parece
• complement: perigosa

You might hear different word orders in literary or emphatic language, but for everyday Portuguese, this version is the one to learn and use.