Интервью начинается сегодня.

Интервью is an indeclinable loanword in Russian, so its form does not change for case, and in many contexts the singular and plural look identical.

In this sentence, it is singular because the verb is singular: начинается = begins / is beginning.

Its grammatical gender is usually neuter:

• интересное интервью = an interesting interview

So here интервью is the subject of the sentence, in the nominative singular.

Начинается is the 3rd person singular form of начинаться.

It matches the subject:

• интервью начинается = the interview begins
• интервью начинаются = the interviews begin

Even though интервью does not visibly look singular to an English speaker, the verb shows you that it is singular here.

The -ся ending often comes from a reflexive meaning, but here it is best understood as part of the verb начинаться, which means to begin / to start.

Compare:

• начинать = to start something
• начинаться = to begin / to start

So:

• Он начинает интервью. = He starts the interview.
• Интервью начинается. = The interview begins.

In this sentence, -ся does not mean the interview is literally doing something to itself. It is just the normal verb used for events beginning.

Russian often uses the present tense of an imperfective verb for scheduled or expected events, much like English can say:

• The interview starts today.

So Интервью начинается сегодня can mean:

• The interview begins today
• The interview is starting today

If you want to focus more clearly on the one-time future starting point, Russian can also use the perfective future:

• Интервью начнётся сегодня.

Very roughly:

• начинается = more like starts / is starting
• начнётся = more like will begin

Both can work, but начинается сегодня sounds natural for a scheduled event.

Сегодня here is not a noun in a case form. It is an adverb, meaning today.

So in:

• Интервью начинается сегодня.

сегодня simply tells you when the action happens. It does not need a preposition, and it does not change form here.

Yes. Russian word order is fairly flexible, and changing it changes the focus more than the basic meaning.

For example:

• Интервью начинается сегодня. = neutral statement
• Сегодня начинается интервью. = emphasizes today
• Интервью сегодня начинается. = possible, with special emphasis or rhythm

The most neutral version is the one you were given.

Russian has no articles, so there is no direct equivalent of a or the in most sentences.

So Интервью начинается сегодня could theoretically mean:

• The interview starts today
• An interview starts today

Usually the context tells you which one is meant. In many real situations, English would naturally translate it as the interview starts today.

The stress is:

• интервью́
• начина́ется
• сего́дня

So the whole sentence is:

интервью́ начина́ется сего́дня

A rough English-style pronunciation guide would be:

• интервью́ ≈ een-teer-VYU
• начина́ется ≈ nuh-chee-NA-ye-tsa
• сего́дня ≈ see-VOD-nya

The most important thing for a learner is usually to remember the stressed syllables:

• final syllable in интервью́
• -на́- in начина́ется
• -го́- in сего́дня