"Rawad and Judy"
Do you mean a line on top of a letter such as وَ? It is called as "fatHa" which means a sign that the respective letter should be pronounced with the short "a" sound. So, وَ is "wa" and رَ is " ra" (or actually, in the case of ر, it is "ro" like in the English word "road" because there is no "ra" sound like "run" in English). However, this line (and any other diacritic marks) is optional -- we can omit it. But, for beginners, it is helpful a lot.