Arkadaşına benden selam söyle.

Arkadaşına is built from arkadaş (friend) plus endings.

In this sentence, it most naturally means to your friend. The form can be analyzed as:

• arkadaş = friend
• -ın / -in / -un / -ün = your
• -a / -e = to

So:

• arkadaşın = your friend
• arkadaşına = to your friend

A useful thing to know: arkadaşına can also look the same as to his/her friend in Turkish. Context usually tells you which meaning is intended.

That n is a buffer consonant.

When a noun already has a possessive ending and then another ending beginning with a vowel is added, Turkish often inserts -n- to make pronunciation smoother.

So instead of something awkward, Turkish gives you:

• arkadaşın + a → arkadaşına

You will see this linking -n- in many similar forms.

Benden means from me.

It is:

• ben = I / me
• -den / -dan = from

So:

• benden = from me

In this sentence, benden tells you the greeting is coming from me:

• Arkadaşına benden selam söyle.
• Tell your friend hi from me.

Because selam söylemek is a very common Turkish expression meaning:

• to say hi
• to give/send regards
• to pass on greetings

Literally, söylemek means to say / tell, but in Turkish you often combine it with selam:

• selam söylemek = to send greetings / say hi to someone

So selam söyle is the natural phrase here, not just söyle on its own.

Yes. Söyle is the informal singular imperative of söylemek (to say / tell).

So it means:

• say
• tell
• give

In this sentence, it is a direct command/request to one person:

• Arkadaşına benden selam söyle.
• Tell your friend hi from me.

Depending on tone, this can sound perfectly normal and friendly. If you want to sound softer or more polite, Turkish often uses forms like:

• Arkadaşına benden selam söyler misin? = Could you tell your friend hi from me?
• Arkadaşınıza benden selam söyleyin. = Tell your friend hi from me. (plural or formal)

Because Turkish often drops subject pronouns when they are understood from context.

English usually needs you:

• Tell your friend hi from me.

Turkish usually does not need sen here. The command form söyle already makes it clear that the speaker is talking to you.

If you said sen, it would usually be for extra emphasis, not because it is required.

Yes. Turkish word order is fairly flexible, although the verb often comes at the end.

The original sentence:

• Arkadaşına benden selam söyle.

is completely natural.

You could also hear:

• Benden arkadaşına selam söyle.

Both mean basically the same thing, but the emphasis changes a little. Putting benden earlier can highlight from me more strongly.

So the order can move, but the endings still show the grammatical roles.

Because they are different case endings with different meanings.

• -a / -e = to
• -dan / -den / -tan / -ten = from

So:

• arkadaşına = to your friend
• benden = from me

The exact vowel changes because of vowel harmony, which is a major feature of Turkish. That is why endings appear in different shapes.

Yes. Selamımı söyle means say my hello / give my regards.

Compare:

• benden selam söyle = say hi from me
• selamımı söyle = give my greetings

Both are natural. The first one is very common and conversational. The second one is a little more explicit because it includes -ım (my) on selam:

• selamım = my greeting
• selamımı = my greeting(s) as the object

So both work, with only a small difference in style.

It can be either, depending on context.

In a sentence like this, selam can be translated as:

• hi
• hello
• my regards
• greetings

So Arkadaşına benden selam söyle could be understood as:

• Tell your friend hi from me.
• Give your friend my regards.

English chooses different words depending on tone, but the Turkish phrase covers this whole idea very naturally.