وَ«سَلَامٌ عَلَيْكَ».
Translation: Peace be upon you.
سَلَامٌ: nominative indefinite mubtadaʾ in a supplicatory/greeting expression.
عَلَيْكَ: «عَلَى» is a preposition, «كَ» a bound genitive pronoun; the prepositional phrase serves as khabar.
The sentence functions as a wish or greeting, making the indefinite opening meaningful.