"Меня" - genitive of a word "Я" I. They can see me (они видят меня)
"Вас" - genitive from "Вы". "Тебя" - genitive from "ты".
The difference is that "Вы" is a polite (respectful) form comparing to "Ты".
Like "Sie"-"Du" in german, "Ni"-"Du" in Swedish etc etc
Remember, that "Вы" may also be a plural.