Dün kapıyı kapatırken parmağımı çarptım, şimdi biraz acıyor.

Because kapı is the direct object of kapatmak (to close), and it is a specific door, so Turkish uses the accusative ending.

• kapı = door
• kapıyı = the door / that particular door

The -yı is the accusative suffix, and the y is just a buffer consonant because kapı ends in a vowel.

So:

• kapı kapatmak = to close a door / doors in general
• kapıyı kapatmak = to close the door

Because kapatmak is the transitive verb: to close something.

• kapatmak = to close something
• kapanmak = to close / to become closed

In this sentence, the person is actively closing the door, so Turkish uses kapatmak.

Compare:

• Kapıyı kapattım. = I closed the door.
• Kapı kapandı. = The door closed.

kapatırken means while closing or when I was closing.

It connects the action of closing the door with the main action of hitting the finger.

So:

• kapıyı kapatırken = while closing the door

This tells you the finger injury happened during that action.

It is built from the verb kapatmak plus the -ken structure meaning while / when.

A simple way to think of it is:

• kapat- = close
• kapatır = closes / would close
• kapatırken = while closing

In many verbs, this form comes from the aorist/present stem plus -ken.

A few useful comparisons:

• gelirken = while coming
• giderken = while going
• yaparken = while doing
• kapatırken = while closing

parmağımı means my finger as a specific direct object.

It breaks down like this:

• parmak = finger
• parmağım = my finger
• parmağımı = my finger (as the direct object)

Two things are happening:

1. Possession

   • -ım / -im / -um / -üm means my
   • So parmak becomes parmağım

2. Accusative

   • Because the finger is the specific thing affected by the action, it also takes the accusative
   • So parmağım becomes parmağımı

Also, notice the sound change:

• parmak → parmağım

The final k often softens to ğ before a vowel-initial suffix.

Here çarptım means something like I banged or I hit.

It comes from çarpmak, which can mean to hit, strike, bump into, bang depending on context.

So:

• parmağımı çarptım = I banged my finger / I hit my finger

In English, this usually sounds accidental, and that is also the natural feeling here in Turkish.

Because Turkish often leaves out information that is already obvious from context.

Here, since the sentence already says while closing the door, it is easy to understand that the finger got banged on the door.

A fuller version could be:

• Dün kapıyı kapatırken parmağımı kapıya çarptım.

That would mean Yesterday, while closing the door, I hit my finger on the door.

Notice that in that fuller version, the second kapıya takes the dative ending -ya, because it is the thing the finger was hit against.

Because the thing that hurts is understood to be the finger, not I.

Turkish often expresses pain by making the body part the subject:

• Parmağım acıyor. = My finger hurts.
• Kolum acıyor. = My arm hurts.
• Başım ağrıyor. = My head hurts.

So in this sentence, acıyor means it hurts, with parmağım understood from the previous clause.

If you said acıyorum, that would usually not be the normal way to say my finger hurts. It can mean something different depending on context, often I feel pity or I feel sorry.

So here:

• şimdi biraz acıyor = now it hurts a little

with the implied subject being my finger.

Both can often translate as hurts, but they are not always used in exactly the same way.

• acımak / acıyor often suggests a more immediate, sharp, stinging, or tender pain
• ağrımak / ağrıyor often suggests aching or ongoing pain

After banging your finger, acıyor sounds very natural because it suggests that fresh, sharp hurt.

For example:

• Parmağım acıyor. = My finger hurts.
• Başım ağrıyor. = My head aches / I have a headache.

In real life, there can be overlap, but acıyor fits this sentence very well.

Because Turkish usually leaves out subject pronouns when the verb already shows the person.

• çarptım already means I hit / I banged
• parmağımı already includes my
• so ben is unnecessary unless you want emphasis

Compare:

• Parmağımı çarptım. = I banged my finger.
• Ben parmağımı çarptım. = I banged my finger. / I was the one who banged my finger.

The second version sounds more emphatic.

Yes, Turkish word order is somewhat flexible, but this sentence uses a very natural order.

• Dün = yesterday
• kapıyı kapatırken = while closing the door
• parmağımı çarptım = I banged my finger
• şimdi biraz acıyor = now it hurts a little

This order works well because Turkish often puts:

1. time expressions early
2. background/context before the main verb
3. the main verb near the end of its clause

You could also say:

• Dün kapıyı kapatırken parmağımı çarptım. Şimdi parmağım biraz acıyor.

That is slightly fuller and makes the subject of acıyor explicit.