Kapıyı açınca arkadaşım şaşırmış göründü.

Because kapıyı is the definite direct object form of kapı (door).

• kapı = door
• kapıyı = the door

In Turkish, a specific/directly identified object usually takes the accusative ending. Here, the speaker is talking about a particular door, so kapıyı açmak means to open the door.

Also notice the spelling:

• kapı + -(y)ı → kapıyı

The y is a buffer letter added because the noun ends in a vowel.

Açınca comes from the verb açmak (to open) plus the suffix -ınca / -ince / -unca / -ünce, which often means when, once, or upon doing something.

So:

• açmak = to open
• açınca = when/once [someone] opened

This suffix creates a kind of time clause:

• Kapıyı açınca... = When [someone] opened the door...

The exact form of the suffix changes because of vowel harmony:

• -ınca
• -ince
• -unca
• -ünce

Good question: açınca by itself does not show person.

So Kapıyı açınca can mean:

• when I opened the door
• when you opened the door
• when he/she opened the door
• etc.

Turkish often leaves the subject to context. In a full conversation, it would usually be clear who opened the door.

In many natural interpretations of this sentence, English would translate it as:

• When I opened the door, my friend looked surprised.

But grammatically, the Turkish form itself does not force I. Context does that.

Because -ım / -im / -um / -üm is a possessive suffix meaning my.

So:

• arkadaş = friend
• arkadaşım = my friend

The exact vowel changes according to vowel harmony. Here it becomes -ım.

This is very common in Turkish:

• evim = my house
• kitabım = my book
• arkadaşım = my friend

So Turkish often expresses possession with a suffix instead of a separate word like my.

Şaşırmış is from şaşırmak (to be surprised, to be confused) with -mış, which is often called the reported/inferential past or a result/state form depending on context.

In this sentence, şaşırmış is not really standing alone as the main verb. It is part of şaşırmış göründü.

That combination means something like:

• looked as if he/she had been surprised
• seemed surprised

So şaşırmış here helps describe the friend’s apparent state.

Why not şaşırdı?

• şaşırdı = he/she got surprised / was surprised
• şaşırmış göründü = he/she looked/seemed surprised

The sentence is not directly stating the inner fact as strongly; it is describing the speaker’s impression based on appearance.

This is a very natural Turkish pattern:

• [participle/adjective-like form] + görünmek
• meaning to seem / to look ...

So:

• şaşırmış = surprised / having been surprised
• göründü = appeared, seemed, looked

Together:

• şaşırmış göründü = looked surprised, seemed surprised

You can think of şaşırmış here as describing the state that was visible.

Similar patterns:

• yorgun göründü = he/she looked tired
• mutlu göründü = he/she looked happy
• kırılmış göründü = he/she looked offended / looked hurt

Because göründü is the main verb of the sentence, and it tells us what happened in the past from the speaker’s point of view.

• görünmek = to appear, to seem
• göründü = appeared / seemed / looked

So the sentence is structured roughly like this:

• Kapıyı açınca = when [someone] opened the door
• arkadaşım = my friend
• şaşırmış göründü = looked surprised

The main event being reported is the appearance: my friend looked surprised.

Not in the same way as the main verb göründü.

Although -mış often has past-related meanings, in this sentence şaşırmış behaves more like a descriptive form inside the expression şaşırmış görünmek.

So it is best understood here as:

• surprised
• as if surprised
• having the appearance of being surprised

In other words, the truly finite, tense-carrying verb of the sentence is göründü, not şaşırmış.

Yes, Turkish word order is flexible, but this order is very natural.

Current order:

• Kapıyı açınca arkadaşım şaşırmış göründü.

This puts the time clause first, then the subject, then the description and main verb.

A rough structure is:

1. When the door was opened / when I opened the door
2. my friend
3. looked surprised

You could change the order for emphasis, for example:

• Arkadaşım kapıyı açınca şaşırmış göründü.

But that version may more strongly suggest that my friend is the one who opened the door, because it is closer to açınca.

So word order can affect what sounds most natural or what interpretation feels strongest, even if the grammar still allows some ambiguity.

In this sentence, yes, arkadaşım is the subject of the main verb göründü.

Why?

Because:

• göründü is an intransitive verb here
• arkadaşım is the noun in the plain form with no case ending marking it as object
• kapıyı is already marked as the direct object of açınca

So the sentence naturally parses as:

• kapıyı = object of opening
• arkadaşım = subject of seeming/looking surprised

Yes. Both are good translations.

• looked surprised focuses a bit more on visible appearance
• seemed surprised is slightly broader and can include the speaker’s impression

In this Turkish sentence, both are reasonable because görünmek can cover both look and seem depending on context.

Here are the main forms:

• kapıyı → dictionary form: kapı = door
• açınca → dictionary form: açmak = to open
• arkadaşım → dictionary form: arkadaş = friend
• şaşırmış → dictionary form: şaşırmak = to be surprised / get confused
• göründü → dictionary form: görünmek = to appear / seem / be visible

This is useful because Turkish often adds several suffixes, so learners need to mentally peel words back to their dictionary forms.