هو يستعير كتابا.

Arabic can often say just the verb: يستعير كتابًا.

That is because يستعير already tells you the subject is he (third person masculine singular). Adding هو is still correct, but it usually gives extra clarity, emphasis, or a topic-comment feel, like As for him, he is borrowing a book.

So:

• يستعير كتابًا = He is borrowing a book
• هو يستعير كتابًا = also He is borrowing a book, but with هو stated explicitly

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

• the present: he borrows / he is borrowing
• the future, if the context shows it
• habitual action: he usually borrows

So by itself, يستعير can mean either he borrows or he is borrowing, depending on context.

In the imperfect, Arabic verbs take different prefixes depending on the subject. The prefix يـ marks third person masculine singular.

So:

• يستعير = he borrows / is borrowing
• if the subject changed, the verb form would change too

That is one reason Arabic can often leave out the separate subject pronoun.

Arabic does not have a separate indefinite article like English a/an.

A noun is usually understood as indefinite when:

• it does not have الـ
• and in fully vowelled Arabic it often has tanwīn (nunation)

So كتابًا means a book, while الكتابَ would mean the book.

The full form is كتابًا (kitāban).

It ends this way because it is:

• an indefinite noun
• functioning as the direct object of the verb

That means it takes the accusative case, which here is shown by tanwīn fatḥ: -ًا / -an.

So:

• كتابٌ = a book (subject form, nominative)
• كتابًا = a book (object form, accusative)

Because it is the direct object of يستعير.

The action is being done to the book: he is borrowing a book. In MSA, direct objects normally take the accusative case.

So in this sentence:

• هو = subject
• يستعير = verb
• كتابًا = direct object in the accusative

This sentence begins with هو, so it has a slightly more explicit, topic-like structure. Very roughly, it is like:

• He — is borrowing a book

Arabic also very naturally allows يستعير كتابًا without هو.

So both are fine, but they feel slightly different:

• يستعير كتابًا = straightforward verbal sentence
• هو يستعير كتابًا = more explicit about the subject

Yes. يستعير كتابًا is a complete and natural sentence in Arabic.

Since the verb already shows he, Arabic does not need the separate pronoun unless there is a reason to include it, such as:

• emphasis
• contrast
• avoiding ambiguity

This is a very common point of confusion:

• يستعير = he borrows
• يُعير = he lends

So:

• هو يستعير كتابًا = He is borrowing a book
• هو يُعير كتابًا = He is lending a book

They are related, but they do not mean the same thing.

Yes. يستعير is a derived verb form, the imperfect of استعار.

A useful beginner-level idea is that verbs beginning with استـ often carry a sense like seeking, requesting, or obtaining for oneself. In this case, that helps explain why استعار means to borrow rather than to lend.

You do not need to master all the morphology yet, but it is helpful to recognize استـ as a common verb pattern.

A common careful pronunciation is:

huwa yastaʿīru kitāban

A few notes:

• هو = huwa
• يستعير = yastaʿīru
• كتابًا = kitāban

The letter ع in يستعير is a consonant that does not exist in English, so many learners need extra practice with it.