يترأس المتحدث حلقة النقاش.

Because verb-first word order is very common in Modern Standard Arabic.

This sentence follows a normal verb–subject–object pattern:

• يترأس = chairs / presides over
• المتحدث = the speaker
• حلقة النقاش = the discussion panel

You could also say المتحدث يترأس حلقة النقاش. That is also correct, but it puts a little more focus on the speaker.

يترأس means he chairs, he heads, or he presides over.

It comes from the verb تَرَأَّسَ, which is related to the root ر-أ-س, connected with the idea of a head. So the basic image is to be at the head of something.

It is the imperfect form, which often corresponds to the present in English, but it can also refer to the future depending on context.

So يترأس المتحدث حلقة النقاش can mean something like:

• The speaker chairs the panel discussion
• The speaker is chairing the panel discussion

If you wanted a clearer future meaning, you could say:

• سيترأس المتحدث حلقة النقاش = The speaker will chair the panel discussion

In this sentence, المتحدث is the subject because it comes after the verb in a normal VSO sentence and, if fully vowelled, it would be in the nominative case:

• يَتَرَأَّسُ الْمُتَحَدِّثُ حَلْقَةَ النِّقَاشِ

Here:

• المتحدثُ = subject, nominative
• حلقةَ = direct object, accusative

In everyday unvowelled writing, learners usually rely on word order and meaning to identify the subject.

المتحدث literally means the one who speaks. In context, it often means:

• the speaker
• the person speaking
• sometimes the spokesperson

It comes from the verb تحدّث = to speak / talk.

In formal or political contexts, المتحدث الرسمي is very common for official spokesperson.

Because حلقة النقاش is an iḍāfa construction, often called a genitive construction.

In an iḍāfa:

• the first noun does not take ال
• the second noun determines whether the whole phrase is definite

So:

• حلقة النقاش = the discussion panel / the discussion session
• حلقة نقاش = a discussion panel / a discussion session

Even though حلقة has no ال, the whole phrase is definite because النقاش is definite.

It is an iḍāfa construction.

Literally, it means something like circle of discussion:

• حلقة = circle, ring, session, panel
• النقاش = the discussion

Together, the phrase means discussion panel, discussion session, or panel discussion, depending on context.

Grammatically:

• حلقةَ is the first part of the iḍāfa
• النقاشِ is the second part and is in the genitive case

Because making the second noun definite makes the whole iḍāfa definite.

So:

• حلقة النقاش = the discussion panel
• حلقة نقاش = a discussion panel

Also, note a pronunciation point: although it is written النقاش, it is pronounced an-niqāsh because ن is a sun letter, so the ل of ال is not pronounced.

That is just a difference between English and Arabic.

In Arabic, يترأس usually takes a direct object without a preposition:

• يترأس الاجتماع = he chairs the meeting
• يترأس اللجنة = he heads the committee
• يترأس حلقة النقاش = he chairs the panel discussion

So English uses over, but Arabic normally does not.

It is pronounced approximately:

yata-raʾʾasu

A few points:

• ya- = ي
• ta- = ت
• raʾʾa- contains a hamza (ء), a glottal stop
• the hamza is effectively doubled in the fully vocalized form تَرَأَّسَ

In normal Arabic writing, short vowels and shadda are often omitted, so you see يترأس, but the fuller form is:

يَتَرَأَّسُ

It would be:

يَتَرَأَّسُ الْمُتَحَدِّثُ حَلْقَةَ النِّقَاشِ

This shows the grammar clearly:

• يَتَرَأَّسُ = imperfect verb, indicative
• الْمُتَحَدِّثُ = subject, nominative
• حَلْقَةَ = direct object, accusative
• النِّقَاشِ = genitive, because it is the second noun in an iḍāfa construction

Yes, absolutely.

Both are correct:

• يترأس المتحدث حلقة النقاش
• المتحدث يترأس حلقة النقاش

The first is more neutral and typically formal in written Arabic.
The second gives more emphasis to المتحدث and matches the subject-first order English speakers are more used to.