المدير يعرف المشرفين الذين يشرحون التعليمات.

Because المشرفين is the direct object of يعرف.

The singular is مشرف. Its regular masculine plural changes by case:

• مشرفون = nominative
• مشرفين = accusative or genitive

Here, يعرف takes a direct object, so Arabic uses the accusative form:

• المديرُ يعرفُ المشرفينَ...

So -ين here is not random; it shows that the supervisors are the ones being known.

الذين is a relative pronoun, meaning who, whom, or that for a masculine human plural noun.

It refers back to المشرفين.

Compare:

• الذي = singular masculine
• الذين = plural masculine (especially for people)

So:

• المشرف الذي يشرح... = the supervisor who explains...
• المشرفين الذين يشرحون... = the supervisors who explain...

Arabic makes the relative pronoun agree with the noun it refers to in number and gender.

The ones doing the explaining are المشرفين.

The verb يشرحون is:

• third person
• masculine
• plural

That matches المشرفين.

So the structure is:

• المدير يعرف المشرفين
• الذين يشرحون التعليمات

In other words: the manager knows the supervisors — the ones who explain the instructions.

It cannot refer to المدير, because المدير is singular, while يشرحون is plural.

Because التعليمات is a sound feminine plural (جمع مؤنث سالم), and that type has a special case pattern.

Its endings are:

• nominative: -اتُ
• accusative: -اتِ
• genitive: -اتِ

So even though التعليمات is the direct object of يشرحون, in fully vowelled Arabic it would be:

• التعليماتِ

not التعليماتَ.

So the fully vocalized sentence would be:

• المديرُ يعرفُ المشرفينَ الذينَ يشرحونَ التعليماتِ

This is a very common point of confusion for learners, because many direct objects do take fatḥa, but sound feminine plurals are different.

Because Arabic allows both subject-first and verb-first word order.

Both of these are grammatical:

• المدير يعرف المشرفين...
• يعرف المديرُ المشرفين...

The version in your sentence is subject-first, which is very common in Modern Standard Arabic, especially in clear expository writing. It can feel a bit closer to English word order.

Very roughly:

• المدير يعرف... = more topic/subject-first
• يعرف المدير... = more classically verbal in feel

Both mean essentially the same thing here.

Because الـ is the Arabic definite article, meaning the.

In this sentence:

• المدير = the manager
• المشرفين = the supervisors
• التعليمات = the instructions

Also, الذين normally follows a definite noun. So when you say المشرفين الذين..., you are talking about the supervisors who..., not just any supervisors.

If the noun were indefinite, Arabic often uses a clause without الذين:

• مشرفون يشرحون التعليمات = supervisors who explain the instructions

But with a definite noun, the relative pronoun is expected:

• المشرفون الذين يشرحون التعليمات

Both are in the imperfect verb form, which often corresponds to the present in English.

So here they usually mean something like:

• يعرف = knows
• يشرحون = explain / are explaining

The exact English translation depends on context, but in a sentence like this, they most naturally express a present or habitual meaning.

The imperfect in Arabic can also be used for future meaning, but usually there is some extra clue, such as:

• سـ
• سوف

Since those are not present here, the normal reading is present.

Not in standard MSA if you keep المشرفين definite.

With a definite noun like المشرفين, standard Arabic uses the relative pronoun:

• المشرفين الذين يشرحون التعليمات

If you remove الذين, the sentence becomes ungrammatical in standard formal Arabic.

However, with an indefinite noun, Arabic can often use a following clause without a relative pronoun:

• يعرف مديرٌ مشرفين يشرحون التعليمات

That would mean something like a manager knows supervisors who explain the instructions.

So:

• definite noun → usually use الذي / الذين / التي...
• indefinite noun → often no relative pronoun

Yes. The main sentence is already complete with:

• المدير يعرف المشرفين

That means the manager knows the supervisors.

Then الذين يشرحون التعليمات adds extra information describing which supervisors:

• the supervisors who explain the instructions

So the relative clause is attached to المشرفين, but it does not replace the main sentence; it just narrows it down.

A fully vocalized version would be:

المديرُ يعرفُ المشرفينَ الذينَ يشرحونَ التعليماتِ

Word by word:

• المديرُ — nominative
• يعرفُ — imperfect indicative
• المشرفينَ — accusative, sound masculine plural
• الذينَ — relative pronoun
• يشرحونَ — imperfect, masculine plural
• التعليماتِ — accusative sound feminine plural

Seeing the vowels can make the grammar much clearer, especially with المشرفين and التعليمات.