Kitap okuyunca daha sakin oluyorum.

Okuyunca comes from:

• oku- = to read
• -yınca / -yince = a suffix meaning when, once, or sometimes whenever

So:

• oku + yunca → okuyunca = when/once I read or when reading

In this sentence, it gives the idea when I read books / when I do some reading.

The exact English translation depends on context. It can sound like:

• When I read, I become calmer
• After reading, I feel calmer
• Whenever I read, I get calmer

The verb stem oku- ends in a vowel. In Turkish, when one suffix beginning with a vowel-like sound attaches after a vowel, a buffer consonant is often inserted to make pronunciation easier.

Here that buffer is y:

• oku-
  • -ınca → okuyunca

This is very common in Turkish.

Compare:

• başla- → başlayınca = when (someone) starts
• uyu- → uyuyunca = when (someone) sleeps / falls asleep

So the y is not part of the root meaning; it is just a linking sound.

Because here kitap is being used in a general, non-specific sense.

• kitap okuyunca = when I read books / when I do reading
• kitabı okuyunca = when I read the book (a specific book)

In Turkish, the accusative ending (-ı, -i, -u, -ü) usually appears when the direct object is specific/definite.

So:

• kitap okumak = to read books / to read a book in general
• kitabı okumak = to read the book

In your sentence, the speaker is talking about reading as an activity, not one specific book.

It is best understood as a generic object.

So in English it could correspond to:

• read a book
• read books
• do some reading

Turkish often leaves this kind of thing less specific than English does.

So Kitap okuyunca daha sakin oluyorum is not really about one particular book. It means something more like:

• When I read, I feel calmer
• Reading makes me calmer

Daha means more, and sakin means calm.

So:

• daha sakin = calmer / more calm

Turkish often uses daha + adjective where English may use a comparative form:

• daha büyük = bigger
• daha iyi = better
• daha sakin = calmer

So the sentence literally has the structure:

• When I read, I become more calm

Natural English would usually be:

• When I read, I become calmer

Turkish often expresses becoming something with:

• adjective/noun + olmak

So:

• sakin olmak = to be calm
• sakin oluyorum = I am becoming calm / I become calm

This is very natural Turkish.

There is also the verb sakinleşmek, which means to calm down / become calm. So a similar sentence could be:

• Kitap okuyunca sakinleşiyorum.

That also works, but it is a slightly different structure.

Your original sentence emphasizes the resulting state:

• I become calmer
• literally, I become more calm

This is a great question, because both can be possible in Turkish, but they give slightly different feels.

• oluyorum = present continuous form
• olurum = aorist / habitual / general truth form

In many Turkish sentences, the present continuous can also express a habitual repeated action, especially in everyday speech.

So:

• Kitap okuyunca daha sakin oluyorum
  = When I read, I get calmer / I become calmer

This sounds natural and personal, like describing your usual experience.

If you said:

• Kitap okuyunca daha sakin olurum

that can also work, and it may sound a bit more like a general rule or regular tendency:

• When I read, I become calmer

So the difference is subtle here. The version with oluyorum is very common in conversational Turkish.

Not always. -yınca / -yince can express several closely related ideas, depending on context:

• when
• once
• after
• whenever

For example:

• Eve gelince beni ara.
  = Call me when you get home.

• Onu görünce şaşırdım.
  = I was surprised when I saw him/her.

• Kitap okuyunca daha sakin oluyorum.
  = When I read, I become calmer
  or Whenever I read, I become calmer

So it is better to think of -yınca as a time-related connector meaning something like upon doing X / when X happens.

In Turkish, the subject is often understood from context and from the main verb ending.

Here the main verb is:

• oluyorum = I become / I am becoming

The ending -um tells you the subject is I.

So the sentence is understood as:

• When I read, I become calmer

In many Turkish subordinate clauses like okuyunca, the subject is inferred from the main clause unless something else is clearly stated.

If you wanted to make the subject extra clear, you could say:

• Ben kitap okuyunca daha sakin oluyorum.

But ben is usually unnecessary unless you want emphasis.

Yes. Turkish word order is flexible, although some versions sound more neutral than others.

The original:

• Kitap okuyunca daha sakin oluyorum.

is very natural.

You could also say:

• Daha sakin oluyorum kitap okuyunca.

This is possible, but it may sound more marked or conversational, with extra emphasis on the result.

You could also add the subject for emphasis:

• Ben kitap okuyunca daha sakin oluyorum.

Turkish often places the most important or focused information near the end, but there is no single rigid word order like in English.

Yes, you could, and it would be natural.

Compare:

• Kitap okuyunca daha sakin oluyorum
• Kitap okuduğumda daha sakin oluyorum

Both can mean something like:

• When I read, I become calmer

But there is a slight difference in feel:

• -yınca often feels a bit more like when/once/whenever that happens
• -dığında / -duğumda often feels a bit more neutral or explicit as when I do / when I am doing

So:

• okuyunca = slightly more compact and event-like
• okuduğumda = slightly more explicitly when I read

Both are common and correct.

Normally, it sounds like a general repeated experience or personal tendency:

• When I read, I become calmer
• Reading makes me calmer

It does not usually sound like a one-time event unless the wider context makes it clear.

If the speaker wanted to refer to one specific past event, they would usually use a different structure, for example with past tense:

• Kitap okuyunca daha sakin oldum.
  = When I read, I became calmer.

So your original sentence most naturally describes something that is generally true for the speaker.

Yes, depending on context, it can suggest either:

• when I read
• once I read
• after I read

Turkish does not always separate these as sharply as English does.

In this sentence, the most natural understanding is a general one:

• When I read, I become calmer

But in another context, -yınca can lean more toward after:

• Yemek yiyince uyuyorum.
  = After I eat, I sleep / I get sleepy after eating.

So the exact nuance comes from the whole sentence and situation, not just the suffix alone.