Ben arkadaşımın evinde çay içiyorum.

You can usually drop Ben.

Turkish often leaves out subject pronouns because the verb ending already shows who is doing the action.

• içiyorum = I am drinking
• the -um ending tells us the subject is I

So:

• Ben arkadaşımın evinde çay içiyorum. = correct
• Arkadaşımın evinde çay içiyorum. = also correct, and often more natural

You keep Ben when you want emphasis, contrast, or clarity:

• Ben arkadaşımın evinde çay içiyorum, o kafede kahve içiyor. = I’m drinking tea at my friend’s house, and he/she is drinking coffee at the café.

arkadaşımın breaks down like this:

• arkadaş = friend
• -ım = my
• -ın = genitive ending, roughly of

So:

• arkadaşım = my friend
• arkadaşımın = my friend’s / of my friend

In Turkish, possession like my friend’s house is usually made with:

1. the possessor in the genitive
2. the possessed thing with a possessive ending

So in this sentence:

• arkadaşımın = my friend’s
• evi = his/her house or, in this structure, the house of my friend

Together:

• arkadaşımın evi = my friend’s house

Because this is not just in a house; it is in my friend’s house.

Let’s break it down:

• ev = house, home
• ev-i = his/her house / the house of
• ev-i-n-de = in his/her house / in the house of

So:

• evde = at home / in the house
• arkadaşımın evinde = at my friend’s house

The -i is the possessive marker on ev, and the -de is the locative ending in/at. The n is a buffer consonant between those endings.

-de / -da is the locative suffix, meaning in, at, on depending on context.

Examples:

• evde = at home / in the house
• okulda = at school
• masada = on the table

In your sentence:

• evinde = in/at his/her house
• arkadaşımın evinde = at my friend’s house

Why -de and not -da? Because of vowel harmony: ev has the front vowel e, so the suffix appears as -de.

This is a very common question.

In Turkish, a bare direct object often means something indefinite or non-specific.

So:

• çay içiyorum = I’m drinking tea / I’m having tea
• çayı içiyorum = I’m drinking the tea (a specific tea)

In your sentence, çay is general or non-specific, so it stays bare.

Compare:

• Kitap okuyorum. = I’m reading a book / reading books
• Kitabı okuyorum. = I’m reading the book

So çay içiyorum is the natural choice for I’m drinking tea.

içiyorum comes from the verb içmek, which means to drink.

Breakdown:

• iç- = drink
• -iyor- = present continuous marker
• -um = I

So:

• içiyorum = I am drinking

This tense is very common for actions happening now:

• yiyorum = I am eating
• gidiyorum = I am going
• okuyorum = I am reading

It can also sometimes be used more broadly for present-time situations, not only actions happening at this exact second.

The present continuous suffix is basically -iyor / -ıyor / -uyor / -üyor, depending on vowel harmony.

With iç-, the form becomes:

• iç + iyor + um → içiyorum

Turkish often inserts a vowel before -yor, so learners usually treat the whole tense ending as:

• -iyor
• -ıyor
• -uyor
• -üyor

The version depends on the vowel in the verb stem.

For example:

• geliyorum = I am coming
• bakıyorum = I am looking
• oturuyorum = I am sitting
• görüyorum = I am seeing

So içiyorum is just the regular present continuous form of içmek.

The neutral Turkish word order is usually Subject – Object – Verb, and that is what you have here:

• Ben = subject
• arkadaşımın evinde = place
• çay = object
• içiyorum = verb

So the sentence is very natural.

Turkish word order is flexible, though. You can move parts around for emphasis:

• Arkadaşımın evinde çay içiyorum.
• Çay içiyorum arkadaşımın evinde.
• Ben çay içiyorum arkadaşımın evinde.

These are possible, but they may sound more marked, depending on context.

One thing stays very common in Turkish: the verb often comes at the end in neutral sentences.

This is because of vowel harmony, one of the most important features of Turkish.

Suffixes often change their vowel to match the vowels in the word they attach to.

Examples from your sentence:

• arkadaşımın
  • -ım = my
  • -ın = genitive
• evinde
  • -de = locative
• içiyorum
  • -um = I

You do not memorize just one form of each suffix; you learn the pattern.

For example:

• evde but okulda
• benim kitabım but benim gözüm
• arkadaşımın but okulun

At first this seems difficult, but it becomes very predictable with practice.

No, that would not mean the same thing, and it would sound wrong for the meaning you want.

You need arkadaşımın because you want my friend’s.

Compare:

• arkadaşımın evinde = at my friend’s house

But:

• arkadaşım evinde more naturally means = my friend is at home / in his or her house

So the -ın on arkadaşımın is essential. It marks the possessor.

Yes, that is a good way to understand it.

Turkish possession often works like this:

• possessor + genitive
• possessed noun + possessive suffix

So:

• arkadaşımın evi literally = the house of my friend natural English = my friend’s house

This structure is extremely common:

• annemin arabası = my mother’s car
• öğretmenin kitabı = the teacher’s book
• çocuğun oyuncağı = the child’s toy

So your sentence is using a very basic and important Turkish pattern.