The correct vowel endings damma, kasra, fatha in Arabic can be a headache. If you are careless, you could turn verse 9:3 of the Qur'an into blasphemy (kufr).
The و does not always mean "and". The waw of accompaniment (واو الحال). Such constructions are tricky as we need different words in English.
What's the function of وَ in the saying: كُلُّ عامٍ وَأَنْتُمْ بِخَيْرٍ? It is a dubious one. Most grammarians say that you don't need the وَ and that it would be of better Arabic style to skip it! Let's see why.