Дуэт начинается сегодня.

The duet begins today.

Breakdown of Дуэт начинается сегодня.

• сегодня: today
• начинаться: to begin
• дуэт: the duet

Questions & Answers about Дуэт начинается сегодня.

What case is дуэт in, and why?

Дуэт is in the nominative singular.

Why:

• It is the subject of the sentence — the thing that is doing the action of beginning.
• In Russian, the subject of a normal sentence is usually in the nominative case.

So in Дуэт начинается сегодня, дуэт = the duet / the duo as the subject.

It is also a masculine noun, because it ends in a consonant.

Why is the verb начинается and not just начинает?

Начинается comes from начинаться, which means to begin / to start.

The ending -ся is important here. It often makes a verb:

• reflexive,
• or more loosely, intransitive / centered on the event happening itself.

Compare:

• начинать что-то = to begin something
• начинаться = to begin, to start

So:

• Оркестр начинает концерт. = The orchestra begins the concert.
• Концерт начинается. = The concert is beginning / begins.

In your sentence, the duet is not beginning something else; the duet itself is starting. So начинается is the natural form.