Meu sonho é viajar.

Because sonho is a masculine noun in Portuguese, and the possessive has to agree with the noun.

• meu sonho = my dream
• minha casa = my house

So the choice is based on the gender of sonho, not on the gender of the speaker.

Here, sonho is a noun meaning dream.

A useful thing to know is that sonho can also be a verb form:

• eu sonho = I dream

So context matters:

• Meu sonho é viajar. → sonho = noun
• Eu sonho todas as noites. → sonho = verb

É is the 3rd person singular of the verb ser (to be).

The subject is meu sonho, which is singular, so Portuguese uses é:

• Meu sonho é viajar.
• Seus sonhos são viajar e conhecer o mundo.

So this is the normal way to say X is Y.

Because after é, Portuguese often uses the infinitive to express an action as an idea, goal, or concept.

• viajar = to travel
• viaja = travels / travel (finite verb)
• viajando = traveling

In this sentence, traveling/to travel is being treated as the thing that the dream consists of, so the infinitive is the natural form:

• Meu sonho é viajar.

This is similar to English My dream is to travel.

Yes, O meu sonho é viajar is also correct.

In Brazilian Portuguese, possessives can appear:

• with an article: o meu sonho
• without an article: meu sonho

Both are common. The version without the article often sounds a little more direct or natural in simple statements, but both are fine.

Because in this structure, ser + infinitive does not need de.

• Meu sonho é viajar. = correct

You do often see de with sonho in other structures, for example when dream of... works like a noun phrase:

• O sonho de viajar pelo mundo... = The dream of traveling the world...

So:

• Meu sonho é viajar. → statement of identity/equivalence
• O sonho de viajar... → noun phrase with de

A rough Brazilian pronunciation is SON-yoo, but that is only an approximation.

A few details:

• nh makes a sound like the ny in canyon
• the o at the end is usually pronounced like a weak oo sound in Brazilian Portuguese

So sonho sounds roughly like SOHN-yoo.

The accent shows both stress and pronunciation.

• é is pronounced like eh
• it is different from e, which usually means and

So:

• é = is
• e = and

That accent is important because it changes both the meaning and the pronunciation.

Yes. Viajar é meu sonho is grammatically correct.

The difference is mainly focus:

• Meu sonho é viajar. → focuses first on my dream
• Viajar é meu sonho. → focuses first on traveling

The first version is probably the most neutral and common in everyday speech.

It normally expresses a personal aspiration or life dream, not a dream during sleep.

So Meu sonho é viajar usually means something like:

• My dream is to travel
• My big goal is to travel

If you want to talk about dreaming in your sleep, the context would usually make that clear, and Portuguese would often use different wording.

Absolutely. This sentence is a very common pattern, and you can expand it easily.

Examples:

• Meu sonho é viajar pelo mundo. = My dream is to travel the world.
• Meu sonho é viajar para o Brasil. = My dream is to travel to Brazil.
• Meu sonho é viajar com a minha família. = My dream is to travel with my family.

So Meu sonho é + infinitive is a very useful structure for talking about goals and ambitions.