This is the 486th most frequent Serbian word.
лепо
"Лепо" means "beautifully" or "nicely" in English.
Here, 'лепо' functions as an adjective describing the noun 'цвеће', meaning 'beautiful'.
Ово је лепо цвеће.
This is beautiful flower.
In this sentence, 'лепо' is used as an adverb, describing the manner of the experience at the beach, meaning 'nice'.
Било је заиста лепо на плажи.
It was really nice at the beach.
Here, 'лепо' is an adverb again, implying 'in a nice manner' and modifying the verb 'понашај'.