Kızım bu yıl liseye başladı.

Kız means girl or daughter. The ending -ım is the 1st person singular possessive suffix, so kızım means my daughter.

Breakdown:

• kız = daughter/girl
• -ım = my

So kızım = my daughter.

Yes. Out of context, kızım can also mean I am a girl, because Turkish can attach the 1st person copular ending to a noun.

For example:

• Ben kızım. = I am a girl.

It can also be used when addressing someone:

• Kızım, buraya gel. = My daughter / girl, come here.

But in Kızım bu yıl liseye başladı, it clearly means my daughter, because the verb is başladı = she/he started. If the subject were I, the verb would be başladım.

Bu yıl means this year.

Breakdown:

• bu = this
• yıl = year

It functions as a time expression, telling you when the action happened.

Because başlamak usually takes the dative case when it means to start something such as a school level, course, or activity.

So:

• lise = high school
• liseye = to high school

In Turkish, liseye başlamak is the normal way to say to start high school.

Because -de/-da is the locative case, meaning in/at/on. That is not the usual pattern with başlamak in this meaning.

Compare:

• liseye başladı = started high school
• lisede başladı = started at/in the high school

The second version sounds more like something happened physically at the high school, or started within that location/institution. For entering a new school stage, Turkish normally uses dative: liseye başladı.

That y is a buffer consonant.

The noun lise ends in a vowel, and the dative suffix also begins with a vowel:

• lise
• -e

Turkish usually inserts y between two vowels:

• lise + e → liseye

This happens in many words:

• okula (no buffer needed, because okul ends in a consonant)
• arabaya = to the car
• masaya = to the table

Because of vowel harmony.

The dative suffix has two forms:

• -a
• -e

Which one you use depends on the last vowel of the noun. Since lise has the front vowel e, the suffix becomes -e.

So:

• okul → okula
• ev → eve
• lise → liseye

Başladı breaks down like this:

• başla- = start / begin
• -dı = past tense

So başladı means started.

There is no extra personal ending here because 3rd person singular in the simple past is often just the tense form by itself:

• başladım = I started
• başladın = you started
• başladı = he/she/it started

This is also due to Turkish sound rules.

The past tense suffix changes according to vowel harmony and consonant voicing:

• -dı / -di / -du / -dü
• -tı / -ti / -tu / -tü

In başladı:

• the last vowel in başla- is a, so the vowel in the suffix becomes ı
• the suffix starts with d here, not t, because it follows a vowel

So:

• başla-
  • -dı → başladı

Because liseye başlamak already naturally means to start high school or to begin attending high school.

Turkish often expresses this idea without an extra verb. English does something similar:

• My daughter started high school this year.

If you say:

• liseye gitmeye başladı

that means she started going to high school, which focuses more on the action of going regularly. It is possible, but liseye başladı is the normal, simpler way to express entering that school stage.

No, Turkish word order is flexible, although the verb often comes at the end in a neutral sentence.

This sentence has:

• Kızım = subject
• bu yıl = time expression
• liseye = dative complement
• başladı = verb

A very natural order is:

• Kızım bu yıl liseye başladı.

But you could also say:

• Bu yıl kızım liseye başladı.

That still means the same thing, but it gives slightly different emphasis. Turkish often moves words around to highlight what is most important in the sentence.

Because Turkish does not have articles like English a/an/the.

A bare noun is often enough:

• lise = high school / the high school, depending on context

If Turkish wants to be more specific, it can use other words such as:

• bir = a / one
• bu = this
• o = that

But in this sentence, liseye is completely normal without any article.

The letter ı is a very common Turkish sound and it does not exist exactly in standard English.

It is:

• a vowel
• made with the tongue high and toward the back
• with no lip rounding

Very rough approximations:

• kızım ≈ kuh-zuhm (not exact)
• başladı ≈ bash-luh-duh (not exact)

The important thing is that ı is not like English ee or ih. It is a separate Turkish vowel, and learning to hear it clearly will help a lot.