This is the 2714th most frequent Turkish word.
üstelik
"Üstelik" means "moreover" or "what's more" in English.
In this sentence, 'üstelik' is used to add additional emphasis to the necessity of preparing the presentation, augmenting the previously stated need to work a lot.
Bugün çok çalışmam gerekiyor, üstelik sunumumu hazırlamam gerek.
I need to work a lot today; moreover, I need to prepare my presentation.
Here, 'üstelik' highlights the provided additional positive aspect of the experience: the promptness of the service.
Bu yemek çok lezzetliydi, üstelik servis de çok hızlıydı.
The food was very delicious; moreover, the service was very fast.
In this sentence, 'üstelik' is used to underline the extra significance of dedicating personal time to the act of assisting.