Depois que o dueto começa, o vocalista canta.

Depois by itself usually means afterward / later.

When you want to say after followed by a whole clause with a verb, Portuguese commonly uses depois que:

• Depois que o dueto começa, o vocalista canta. = After the duet begins, the vocalist sings.

If you use only depois, it normally needs a different structure, for example:

• Depois do início do dueto, o vocalista canta. = After the beginning of the duet, the vocalist sings.
• Depois de começar o dueto, ... = After the duet starts / after starting the duet...

So depois que is natural here because it introduces a full clause: o dueto começa.

Portuguese often uses the present tense for:

• general truths
• habitual actions
• descriptions of events in a sequence
• instructions or narration

So this sentence can sound like:

• Whenever the duet starts, the vocalist sings
• After the duet starts, the vocalist sings

It does not have to mean only the present moment. It can describe a repeated pattern or the normal order of events.

The accent in começa shows both pronunciation and stress.

The verb is começar = to begin / to start.
In the ele/ela/você form of the present tense:

• eu começo
• você/ele/ela começa
• nós começamos

The ç is called cedilha. It makes the c sound like s before a, o, or u.

So começa is pronounced roughly like:

• ko-MEH-sa

Without the cedilla, c before a would sound like k, which would be wrong.

The comma separates the introductory subordinate clause from the main clause:

• Depois que o dueto começa, o vocalista canta.

This is very common in Portuguese, just like in English when a clause comes first:

• After the duet begins, the vocalist sings.

If the order were reversed, the comma would often disappear:

• O vocalista canta depois que o dueto começa.

Vocalista can refer to a male or female vocalist. The noun itself often stays the same.

The gender is usually shown by the article:

• o vocalista = the male vocalist
• a vocalista = the female vocalist

So in your sentence, o vocalista tells us the singer is male.

Usually, no—not in this sentence.

Portuguese uses definite articles more often than English. Here, o dueto and o vocalista sound natural because we are talking about specific participants in the situation.

• Depois que o dueto começa, o vocalista canta.

If you remove the articles:

• Depois que dueto começa, vocalista canta.

that sounds unnatural or incorrect in normal Portuguese.

Yes, but the structure changes a little.

Após is more formal than depois de/depois que. You will often see:

• Após o início do dueto, o vocalista canta.
• Após o dueto começar, o vocalista canta.

Using após que is generally not the normal choice here. For everyday Brazilian Portuguese, depois que is much more natural.

In a literal word-for-word sense, que often means that, but here it is part of the fixed connector depois que, which means after when followed by a clause.

So it is better to learn:

• depois que = after

rather than trying to translate que separately in this sentence.

Usually depois que is followed by the indicative when the action is seen as real or factual:

• Depois que o dueto começa, o vocalista canta.

That is why you see começa, not a subjunctive form.

In many everyday cases, depois que is used with the indicative in Brazilian Portuguese. Learners mainly need to remember that in sentences like this one, the normal form is the indicative.

Dueto is a correct and natural word, especially in musical contexts.

Depending on context, Brazilians might also use:

• dupla = duo / pair
• duo = duo
• canção em dueto = song in duet form / duet song

But if you mean two performers singing or playing together in a musical piece, dueto is perfectly good.

Yes. A very natural alternative is:

• O vocalista canta depois que o dueto começa.

The meaning stays basically the same. The difference is mainly focus and rhythm:

• Depois que o dueto começa, o vocalista canta.
  This emphasizes the time sequence first.

• O vocalista canta depois que o dueto começa.
  This starts with the main action.

A rough pronunciation guide is:

• Depois que o dueto começa, o vocalista canta.
• deh-POYS kee oo doo-EH-too ko-MEH-sa, oo voh-kah-LEES-tah KAHN-tah

A few notes:

• depois has a strong final -oys sound.
• que here sounds like kee.
• dueto usually has four syllables: du-e-to.
• vocalista is stressed on lis: vo-ca-LIS-ta.
• In natural speech, words may link together, especially que o and começa, o.

It shows an order of events:

1. the duet begins
2. the vocalist sings

So the vocalist’s singing happens after the duet has started, not before.

Depending on context, it can describe:

• a repeated pattern
• the normal structure of a performance
• a narrative sequence

It does not necessarily mean there is a long delay; it simply marks what comes next.