This is the 32nd most frequent Serbian word.
српске
"Српске" means "Serbian" (feminine plural form).
In this sentence, 'српске' is used as an adjective to describe something related to Serbia, specifically qualifying the noun 'цркве' (churches) to mean Serbian churches.
Посетили смо српске цркве у Београду.
We visited the Serbian churches in Belgrade.
Here, 'српске' functions as an adjective modifying the noun 'песме' (songs), indicating that the songs are related to Serbia or are in the Serbian language.
Слушали смо српске песме на фестивалу.
We listened to Serbian songs at the festival.
In this example, 'српске' describes the noun 'обичаје' (customs), denoting that the customs are specific to Serbia or its cultural practices.