This is the 855th most frequent Croatian word.
sretan
Happy.
In this sentence, 'sretan' is used in its adverbial form 'sretno' to express a state of happiness.
Osjećam se sretno danas.
I feel happy today.
Here, 'sretan' describes the subject's feeling of joy in reaction to an event.
Bio je sretan što je položio ispit.
He was happy that he passed the exam.
Here, 'sretan' functions as an adjective expressing a wish of happiness for someone's birthday.