Eu vejo o avião.

Yes. Vejo o avião is also correct.

Portuguese is a language where the verb often already shows who the subject is, and vejo clearly means I see. But in Brazilian Portuguese, speakers often use subject pronouns more than in European Portuguese. So eu may be kept for clarity, emphasis, contrast, or simply because it sounds natural in context.

Vejo is the first-person singular present indicative form of the verb ver.

So:

• eu vejo = I see
• você vê = you see
• ele/ela vê = he/she sees
• nós vemos = we see
• vocês veem = you all see
• eles/elas veem = they see

It is an irregular verb, so you do not say eu vero.

Here o is the definite article, meaning the.

Portuguese usually uses articles more often than English does. With a singular count noun like avião, you normally need some determiner, such as:

• o avião = the airplane
• um avião = an airplane

Just vejo avião would sound unnatural in normal everyday speech.

Because grammatical gender in Portuguese is not based on the first letter of the word.

Avião is a masculine noun, so it takes:

• o avião
• um avião

Its gender is a property of the noun itself. It does not matter that the word begins with a.

Yes, but the meaning changes.

• o avião refers to a specific airplane, usually one already known or identifiable
• um avião means an airplane, one non-specific airplane

So the grammar is the same, but the reference changes from definite to indefinite.

Yes. Vejo o avião is perfectly natural.

In fact, both versions are common:

• Eu vejo o avião
• Vejo o avião

The version with eu can sound a little more explicit or emphatic, depending on the situation.

In Brazilian Portuguese, the unstressed article o is usually pronounced like u.

So o avião sounds roughly like:

u avi-ÃO

That can surprise English speakers, but it is completely normal in Brazilian pronunciation.

A rough English approximation is VEH-zhoo.

More exactly:

• ve sounds like veh
• j sounds like the sound in measure
• final o is usually pronounced like u in Brazilian Portuguese

So vejo is approximately VEH-zhu, or in IPA: /ˈve.ʒu/.

A rough approximation is ah-vee-OWN, but the last part is nasal, so it is not exactly like English own.

The stress is on the last syllable:

a-vi-ÃO

The ending ão is very common in Portuguese and usually takes practice for English speakers.

The tilde marks nasalization.

In avião, the ending ão is pronounced with a nasal vowel, not as a simple a followed by o. This nasal sound is one of the characteristic features of Portuguese pronunciation.

So the tilde is not decorative; it tells you that the vowel sound is different.

Yes, but Eu vejo o avião is the most neutral beginner-friendly order.

The most natural basic patterns are:

• Eu vejo o avião
• Vejo o avião

Other word orders are possible for emphasis, but they are marked and less basic. For a beginner, it is best to stick with the normal subject-verb-object pattern.

Yes.

In more formal standard grammar, you can say:

• Eu o vejo

In everyday spoken Brazilian Portuguese, many people instead say:

• Eu vejo ele

Traditional grammar books usually prefer Eu o vejo, but Eu vejo ele is very common in real speech in Brazil.