Halam gelince, ben de ona bir fincan çay vereceğim.

Hala means paternal aunt: your father's sister.

Halam means my paternal aunt. The -m at the end is the 1st person singular possessive suffix, so:

• hala = aunt
• halam = my aunt

This is very common with family words in Turkish.

Also, Turkish distinguishes between types of aunts:

• hala = father's sister
• teyze = mother's sister

So halam is specifically my father's sister.

Gelince comes from the verb gelmek = to come.

Here it means:

• when she comes
• once she comes
• upon coming

So halam gelince means when my aunt comes.

The ending -ince / -ınca often creates a time clause.

Examples:

• Eve gelince beni ara. = Call me when you get home.
• Onu görünce sevindim. = I was happy when I saw him/her.

Because gelince is not the main verb of the sentence. It introduces a subordinate time clause: when my aunt comes.

The main verb is vereceğim = I will give.

So the structure is:

• Halam gelince = when my aunt comes
• ... vereceğim = I will give ...

This is similar to English, where we also often use a non-future form after when:

• When my aunt comes, I will give her tea.

Not:

• When my aunt will come... ❌

Ben = I

de here means also / too

So ben de means:

• I too
• me too
• I also

It often adds a sense of comparison or participation, as if someone else is also doing something.

For example, the sentence may imply something like:

• Others will offer her something, and I will too
• She will get tea from others, and I will also give her a cup

Because this de means also / too, and in Turkish that is written as a separate word.

So:

• ben de = I too
• ona da = to her too

Do not confuse it with the suffix -de / -da, which means in / at / on and is attached to the word:

• evde = at home
• masada = on the table

So:

• ben de = I too
• bende = on me / with me / in me, depending on context

That difference is very important.

Because the verb vermek = to give normally takes the person receiving something in the dative case, which often corresponds to to someone in English.

So:

• o = he / she / it
• ona = to him / to her / to it

In this sentence:

• ona bir fincan çay vereceğim = I will give her a cup of tea
  literally: I will give a cup of tea to her

The -a / -e ending is the dative ending.

That n is a buffer consonant.

When some case endings are added to pronouns like o, Turkish inserts n to make pronunciation smoother:

• o = he/she/it
• onu = him/her/it
• ona = to him/her/it
• onda = on him/her/it, in him/her/it
• ondan = from him/her/it

So ona is just the normal dative form of o.

Literally, it is:

• bir = one / a
• fincan = cup
• çay = tea

So:

• bir fincan çay = a cup of tea

This is a very common Turkish structure: container/measure + noun.

Examples:

• bir bardak su = a glass of water
• bir tabak pilav = a plate of rice
• bir kilo elma = a kilo of apples

Turkish does not need a word equivalent to English of here.

In bir fincan çay, çay stays in its basic form because this is a measure expression: a cup of tea.

Also, the whole object is indefinite, so it does not take the definite accusative ending.

Compare:

• Bir fincan çay vereceğim. = I will give a cup of tea.
• Çayı vereceğim. = I will give the tea.

In your sentence, the object is not specific in the the sense, so the bare form is natural.

Vereceğim comes from vermek = to give.

It breaks down like this:

• ver- = give
• -ecek = future tense
• -im = I

So the expected form is roughly:

• ver + ecek + im

But Turkish sound changes make it become:

• verecekim → vereceğim

The k in -ecek softens to ğ before a vowel-initial ending.

So vereceğim means:

• I will give

Good question. In Turkish, the ending on the verb already tells you the subject:

• vereceğim = I will give

So ben is not strictly necessary.

The sentence could simply be:

• Halam gelince ona bir fincan çay vereceğim.

Adding ben gives emphasis, contrast, or clarity.

And because it is ben de, the speaker is probably stressing I too.

A natural breakdown is:

• Halam gelince = when my aunt comes
• ben de = I too
• ona = to her
• bir fincan çay = a cup of tea
• vereceğim = I will give

Turkish often puts the verb at the end. That is the most important word-order point here.

So the pattern is roughly:

time clause + subject + indirect object + direct object + verb

This order is very natural, but Turkish word order is flexible.

Yes, Turkish allows quite a lot of flexibility for emphasis or focus, especially before the final verb.

For example, these are possible:

• Halam gelince ben de ona bir fincan çay vereceğim.
• Halam gelince ona ben de bir fincan çay vereceğim.
• Ben de halam gelince ona bir fincan çay vereceğim.

The basic meaning stays similar, but the emphasis shifts.

Usually, the word or phrase placed closer to the verb can receive more focus.

This is about what also/too applies to.

• ben de = I too
• ona da = to her too

So:

• Halam gelince ben de ona bir fincan çay vereceğim.
  = When my aunt comes, I too will give her a cup of tea.

• Halam gelince ona da bir fincan çay vereceğim.
  = When my aunt comes, I will give her a cup of tea too.
  This can imply that I am giving tea to someone else as well, and to her too.

So the position of de matters.

Here it means when, not if.

• gelince = when she comes / once she comes
• gelirse = if she comes

That is an important distinction:

• Halam gelince = when my aunt comes
• Halam gelirse = if my aunt comes

So in your sentence, the arrival is treated as an expected event, not a conditional possibility.

The comma is natural and helpful because Halam gelince is an introductory subordinate clause.

So:

• Halam gelince, ben de ona bir fincan çay vereceğim.

This is clear and standard.

In casual writing, people may sometimes leave out commas, but using one here is a good idea.

Yes, depending on context, -ince / -ınca can feel like:

• when
• once
• upon
• sometimes after

So halam gelince can suggest the moment or point at which she arrives.

In this sentence, the meaning is basically:

• When my aunt comes, I’ll give her a cup of tea
• or Once my aunt arrives, I’ll give her a cup of tea

Those are both natural ways to understand it.