هو يستعمل الحاسوب الجديد في المكتب.

Yes. In Arabic, the verb يستعمل already tells you the subject is he.

So this sentence could also be simply:

يستعمل الحاسوب الجديد في المكتب.

Adding هو can do a few things:

• make the subject extra clear
• add slight emphasis, like he uses it
• sound more natural in some teaching examples

So هو is not strictly necessary here, but it is perfectly correct.

يستعمل is in the imperfect form. In Modern Standard Arabic, the imperfect can express:

• present: he uses / he is using
• habitual action: he uses
• sometimes future, if the context or a future marker shows that

In this sentence, the natural reading is present or habitual: he uses or he is using.

It can mean either one.

Arabic does not always make the same strict distinction that English makes between:

• he uses
• he is using

The context decides. So هو يستعمل الحاسوب الجديد في المكتب could mean:

• He uses the new computer in the office
• He is using the new computer in the office

If you need to emphasize an action happening right now, Arabic often relies on context or extra words rather than a special verb form like English does.

In Arabic, adjectives normally come after the noun they describe.

So:

• الحاسوب الجديد = the new computer

This is the normal order in Arabic:

• noun first
• adjective second

That is different from English, where adjectives usually come before the noun.

Because Arabic adjectives must agree with the noun they describe in definiteness.

Here:

• الحاسوب = the computer → definite
• so the adjective must also be definite:
• الجديد = the new

So:

• الحاسوب الجديد = the new computer

If the noun were indefinite, the adjective would also be indefinite:

• حاسوب جديد = a new computer

Both words have الـ, the Arabic definite article, meaning the.

So:

• الحاسوب = the computer
• المكتب = the office

In this sentence, the speaker is referring to a specific computer and a specific office, not just any computer or any office.

في means in, and المكتب means the office.

Together:

• في المكتب = in the office

This is a prepositional phrase showing location.

So the sentence structure is basically:

• هو = he
• يستعمل = uses / is using
• الحاسوب الجديد = the new computer
• في المكتب = in the office

If fully vocalized in formal grammar, it would be:

هو يستعملُ الحاسوبَ الجديدَ في المكتبِ

The endings show grammatical role:

• يستعملُ: the verb in the indicative, ending in -u
• الحاسوبَ: direct object, so accusative -a
• الجديدَ: adjective matching الحاسوب, so also accusative -a
• المكتبِ: after the preposition في, so genitive -i

In everyday reading and in much speech, these short vowel endings are often not written or not pronounced clearly, but they are important in formal grammar.

In الحاسوب, the الـ is pronounced clearly: al-ḥāsūb.

That is because ح is a moon letter, not a sun letter. So the l sound in الـ stays.

Compare:

• الحاسوب = al-ḥāsūb
• but with a sun letter, like الشمس, the l is not pronounced as a separate l sound

So here you pronounce the article normally.

Yes, you could say يستخدم instead, and many learners will hear it very often.

Both are correct:

• يستعمل = uses
• يستخدم = uses

In many contexts, يستخدم is very common in Modern Standard Arabic, especially in contemporary usage.
So this sentence could also be:

هو يستخدم الحاسوب الجديد في المكتب.

That would still be completely natural.

Yes. In fact, that is often more natural in Arabic.

Because the verb already tells you the subject is he, Arabic often omits the subject pronoun unless there is a reason to include it.

So both are correct:

• هو يستعمل الحاسوب الجديد في المكتب
• يستعمل الحاسوب الجديد في المكتب

The version with هو may sound slightly more explicit or emphatic.

Arabic word order is somewhat flexible.

This sentence uses a clear subject + verb + object + phrase order:

• هو يستعمل الحاسوب الجديد في المكتب

But Arabic often also allows verb-first order:

• يستعمل الحاسوب الجديد في المكتب

You can also move parts for emphasis, especially the prepositional phrase, if the context supports it.

Still, for a learner, the given order is straightforward and easy to understand.

Because it must agree with الحاسوب.

الحاسوب is:

• singular
• masculine
• definite

So the adjective must match:

• الجديد = singular, masculine, definite

This kind of agreement is very important in Arabic adjectives.

It is a standard Modern Standard Arabic word for computer.

You may also hear loanwords such as:

• كمبيوتر
• كومبيوتر

But الحاسوب is a very good formal MSA word and is common in textbooks, news, and formal writing.

So this sentence is good standard Arabic.

Usually it is understood as the location of the action: he uses the new computer in the office.

In other words, في المكتب most naturally tells you where the using happens.

In some contexts, a phrase like this could be interpreted in more than one way, but here the most natural reading is that the action takes place in the office.