Learn Hardcore Turkish: Gündüz parkta kitap okuyorum. - During the day, I read a book in the park.

The suffix -yor (present continuous) usually means “right now” or “these days/currently.” With the time word gündüz (“in the daytime”), it can also mean “during the day (today/these days).”

For a true, timeless habit, Turkish prefers the aorist: Gündüzleri parkta kitap okurum.
For a “current habit/these days,” -yor is fine: Gündüzleri parkta kitap okuyorum.

Why is there no word for “the” or “a”?

Turkish has no definite article, and indefiniteness is usually shown by leaving the noun bare.

kitap okuyorum = “I’m reading a book / I’m reading (some book).”
To emphasize “a/one,” you can add bir: bir kitap.
Definite direct objects take accusative: kitabı okuyorum = “I’m reading the book.”

Why is it parkta and not “parkda” or “parkte”?

The locative suffix is -DA and obeys two rules:

Vowel harmony: da/de (back vs. front vowel).
Consonant voicing: after a voiceless consonant (f, s, t, k, ç, ş, h, p), d becomes t → ta/te. “Park” ends with voiceless k and has a back vowel, so you get parkta.