Bunlar çok eski kitaplar.

Bunlar means these.

It is the plural form of bu (this), but the form is not made by simply adding -lar to get bular. Turkish uses bunlar, with an extra n.

A few useful demonstratives are:

• bu = this
• bunlar = these
• şu = that / this near there
• şunlar = those
• o = that
• onlar = those / they

So bunlar is just the correct standard form to learn as a whole.

The sentence breaks down like this:

• Bunlar = these
• çok = very
• eski = old
• kitaplar = books

So structurally, it is:

• bunlar = the thing being talked about
• çok eski kitaplar = what they are being identified as

In grammar terms, this is a nominal sentence: there is no main action verb like read or go. Instead, one noun phrase is equated with another idea, like These are very old books.

In Turkish, the present-tense form of to be is often not expressed in simple sentences like this.

So:

• Bunlar çok eski kitaplar.
• literally: These very old books.
• natural English: These are very old books.

The idea of are is understood.

This is very common in Turkish. For example:

• Bu bir masa. = This is a table.
• O çok yorgun. = He/She is very tired.

In other tenses, Turkish does show the copula more clearly:

• Bunlar çok eski kitaplardı. = These were very old books.

Because Turkish still normally marks the noun itself as plural when it refers to more than one item.

So:

• bunlar = these
• kitaplar = books

Together, they clearly refer to multiple books.

This is different from some situations in Turkish where the plural is not used, especially after numbers:

• üç kitap = three books
• not üç kitaplar

But in your sentence, kitaplar is the natural form because the predicate is talking about several actual books.

Here, çok means very.

That is because it comes before the adjective eski:

• çok eski = very old

So:

• çok eski kitaplar = very old books

Çok can also mean many / a lot of, depending on what it modifies:

• çok kitap = many books
• çok eski kitap = a very old book
• çok eski kitaplar = very old books

So context and position matter.

Because Turkish adjectives normally come before the noun, just like in English.

Examples:

• eski kitap = old book
• büyük ev = big house
• güzel araba = beautiful car

Here:

• eski describes kitaplar
• çok strengthens eski

So the order is:

• çok eski kitaplar = very old books

This is the normal word order for adjective phrases in Turkish.

No. Turkish adjectives do not agree with the noun in number or gender.

So eski stays eski whether the noun is singular or plural:

• eski kitap = old book
• eski kitaplar = old books

This is simpler than in many European languages. You do not need different adjective endings here.

Bunlar çok eski kitaplar is the more neutral, straightforward order.

Turkish word order is flexible, but changing the order usually changes the focus or emphasis.

• Bunlar çok eski kitaplar. = neutral: These are very old books.
• Çok eski kitaplar bunlar. = more marked/emphatic: These are very old books, with extra focus on very old books

So the version you have is a good basic pattern to learn first.

Yes, and that is also very natural Turkish.

Compare:

• Bunlar çok eski kitaplar. = These are very old books.
• Bu kitaplar çok eski. = These books are very old.

The meaning is very close, but the structure is different.

In Bunlar çok eski kitaplar, the predicate is a noun phrase:

• very old books

In Bu kitaplar çok eski, the predicate is an adjective:

• very old

Both are correct, but they are built differently.

Turkish does not have a word exactly like English the.

It can use bir to mean a/an, but not in the same way as English articles, and not with plural nouns in this kind of sentence.

In your sentence, no article is needed because bunlar already makes the reference definite and clear:

• bunlar = these

So the sentence naturally does not need anything like the.

Because of vowel harmony, a major pattern in Turkish.

The plural suffix has two forms:

• -lar
• -ler

Which one you use depends on the vowel in the word.

A simple rule:

• after a, ı, o, u → use -lar
• after e, i, ö, ü → use -ler

So:

• kitap → kitaplar
• ev → evler

Since kitap contains a, it takes -lar.

It is neutral and completely normal.

You can use it in everyday speech and writing. It sounds like a standard descriptive sentence.

If you wanted, Turkish can sometimes add extra emphasis or a more formal tone with -dir, but it is not necessary here:

• Bunlar çok eski kitaplardır.

That version is more formal or explanatory. For normal conversation, Bunlar çok eski kitaplar is the usual choice.