O soldado chegou cedo.

O is the definite article, meaning the. It agrees with soldado, which is singular and masculine, so you get o soldado.

• o = the for masculine singular nouns
• a = the for feminine singular nouns
• os/as = plural forms

So o soldado is the normal way to say the soldier.

Usually, no. In normal Portuguese, a singular count noun used as the subject normally needs an article or another determiner.

So:

• O soldado chegou cedo. = natural
• Um soldado chegou cedo. = A soldier arrived early
• Soldado chegou cedo. = sounds unusual, telegraphic, or context-dependent

English often allows zero article in places where Portuguese does not.

In this sentence, yes: soldado is treated as a masculine singular noun, and that is why it takes o.

More generally, nouns ending in -o are often masculine in Portuguese, but not always. So -o is a useful clue, not an absolute rule.

Here the important agreement is:

• o
  • soldado

Chegou is the preterite (simple past) of chegar for he/she/it/you-formal.

The verb is:

• infinitive: chegar = to arrive
• preterite, 3rd person singular: chegou = arrived

So o soldado chegou means the soldier arrived.

Because Portuguese usually puts that information inside the verb form itself.

In English:

• arrive / arrived
• sometimes did arrive

In Portuguese:

• chega = arrives
• chegou = arrived

So the ending of chegou already tells you it is past tense. You do not need an extra helper word like did.

Here, cedo is an adverb, meaning early.

It modifies the verb chegou, telling you when the soldier arrived.

Important point:

• cedo does not change for gender or number
• it stays cedo in all cases

Examples:

• Ela chegou cedo.
• Eles chegaram cedo.

In both sentences, cedo stays the same.

Because this is the most neutral and common word order in Portuguese:

subject + verb + adverb

So:

• O soldado = subject
• chegou = verb
• cedo = adverb

Other orders are sometimes possible for style or emphasis, but O soldado chegou cedo is the standard, natural order.

No. The subject is already stated: o soldado.

So:

• O soldado chegou cedo. = complete and natural
• Ele chegou cedo. = He arrived early
• O soldado, ele chegou cedo. = possible only in special emphatic or spoken contexts

Portuguese often leaves out subject pronouns when they are not needed, and here the noun phrase already gives the subject clearly.

A good approximation is:

• chegou ≈ sheh-GOH
• IPA: /ʃeˈɡow/

A few pronunciation notes:

• ch in Brazilian Portuguese usually sounds like sh
• the stress is on the last syllable: che-GOU
• the final -ou is one syllable, not two separate ones

So try something like sheh-GO(w).

A simple approximate pronunciation is:

oo sohl-DAH-doh sheh-GOH SEH-doo

A more natural Brazilian-style idea would be:

• o often sounds like oo when unstressed
• soldado: sohl-DAH-do
• chegou: sheh-GOH
• cedo: SEH-doo

So the whole sentence flows roughly like:

oo sohl-DAH-do sheh-GOH SEH-doo

That is only an approximation, but it is a useful starting point for an English speaker.