Bisküviyi çantama koydum, sonra parkta yedim.

Because bisküviyi is the definite direct object of the verb koydum (I put).

In Turkish, when a specific object is directly affected by the verb, it usually takes the accusative ending. Here:

• bisküvi = biscuit / cookie
• bisküviyi = the biscuit / the cookie as a specific object

The ending here is -(y)i:

• bisküvi
• bisküvi + yi → bisküviyi

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

So the sentence is not just talking about any biscuit, but a specific biscuit.

The y is a buffer consonant.

In Turkish, when a suffix beginning with a vowel is added to a word that already ends in a vowel, Turkish often inserts y to make pronunciation easier.

So:

• bisküvi
  • -i
• becomes bisküviyi, not bisküvii

This happens in many Turkish words:

• arabayı = the car (as object)
• kapıyı = the door (as object)
• masayı = the table (as object)

Çantama means into my bag or to my bag, depending on context.

It is built from:

• çanta = bag
• -m = my
• -a = to / into (dative case)

So:

• çanta → bag
• çantam → my bag
• çantama → to my bag / into my bag

With the verb koymak (to put), the dative often gives the idea of putting something into or onto somewhere.

Because the verb koymak usually takes a destination, not a location.

Compare:

• çantama = to / into my bag → destination
• çantamda = in my bag → location

In this sentence, the action is putting the biscuit somewhere, so Turkish uses the dative:

• çantama koydum = I put it in/into my bag

If you were only describing where something is, you would use the locative:

• Bisküvi çantamda. = The biscuit is in my bag.

Koydum means I put.

It comes from the verb koymak = to put / to place.

Breakdown:

• koy- = verb stem
• -du- = past tense
• -m = I

So:

• koydum = I put

This is the simple past tense, used for a completed action.

Because Turkish often leaves out an object if it is already clear from context.

Here:

• Bisküviyi çantama koydum = I put the biscuit in my bag
• sonra parkta yedim = then I ate [it] in the park

Even though it is not stated in Turkish, it is understood to mean the biscuit.

English often needs the pronoun it, but Turkish can omit it when the meaning is obvious.

If you wanted to repeat it for emphasis or clarity, you could say:

• Bisküviyi çantama koydum, sonra onu parkta yedim.

But in normal Turkish, leaving it out is very natural.

Parkta means in the park or at the park.

It comes from:

• park = park
• -ta = locative ending, meaning in / at / on

So:

• parkta = in the park

The ending appears as -ta rather than -da because of consonant assimilation: after the voiceless consonant k, the suffix begins with t instead of d.

Compare:

• evde = at home / in the house
• okulda = at school
• parkta = in the park

Because yedim (I ate) is happening in the park, not to the park.

Turkish uses:

• -DA / -DE / -TA / -TE for location: in / at / on
• -A / -E for direction: to / toward

So:

• parkta yedim = I ate it in the park
• parka gittim = I went to the park

The verb tells you which case makes sense:

• gitmek often goes with parka (to the park)
• yemek here goes with parkta (in the park)

Sonra means then or afterward.

It connects the two actions in sequence:

1. Bisküviyi çantama koydum = I put the biscuit in my bag
2. sonra parkta yedim = then I ate it in the park

So sonra shows the order of events.

You can think of it as a simple time-linking word.

The given word order is natural, but Turkish word order is more flexible than English.

The sentence:

• Bisküviyi çantama koydum, sonra parkta yedim.

is a normal, clear way to say it.

A few things to notice:

• Turkish often puts the verb at the end of the clause.
• Information before the verb can be moved around for emphasis.

For example, these may also be possible depending on emphasis:

• Bisküviyi çantama koydum, sonra yedim parkta.
  This sounds less neutral and more marked.
• Parkta yedim sonra.
  Also possible in speech, but different in tone.

The original version is the most natural neutral order for a learner to use.

Because Turkish is an agglutinative language. That means it builds meaning by attaching suffixes to words.

In this sentence, several English words are expressed through endings:

• çanta = bag
• çantam = my bag
• çantama = to/into my bag

And:

• park = park
• parkta = in/at the park

So instead of separate words like my, to, or in, Turkish often adds that meaning directly onto the noun.

This is one of the biggest structural differences between English and Turkish.

Yes. Bisküvi is often translated as biscuit, but depending on context it can correspond to what many English speakers, especially Americans, would call a cookie or a cracker-type biscuit.

So the exact English word may vary by context, but the Turkish grammar stays the same:

• bisküvi = biscuit/cookie
• bisküviyi = the biscuit/cookie (as the object)

The original sentence already means that naturally, but a more explicit version could be:

• Bisküviyi çantama koydum, sonra onu parkta yedim.

Here, onu means it / him / her depending on context, and in this sentence it means it.

So:

• Bisküviyi çantama koydum = I put the biscuit in my bag
• sonra onu parkta yedim = then I ate it in the park

Adding onu is grammatically fine, but the original version without it sounds very natural too.