How to say Hello, Hey, Hi:
One can say: Привет, Здравствуй, Здравствуйте, Здарова, and one can also say Приветик, Добрый день, Добрый вечер.
First word in this list is Привет. This is an informal greeting in Russian language, usually Привет is used by the people who know each other. You should not say Привет to a person whom you don’t know at all.
Здравствуй is also a greeting for the people who know each other. It is used less than Привет, but the meaning is the same. Usually this greeting is used by friends.
Здравствуйте is a polite, official, formal greeting. If you meet a person for the first time, if you greet your professor in an university, if you greet a seller in a shop, if you have an official phone call and so on.
Здарова is a slang informal greeting often used by close friends. Usually this greeting is followed by handshaking and this greeting is used only by man to man and very seldom by woman to man (and it is very very seldom by woman to woman).
Приветик is a slang and diminutive form of Привет. Mostly used by young girls.
Добрый день means “Good day” or more correct “Good afternoon”, it can be used for all kinds of greeting listed before. For official, polite, for friends, for lovers and in any cases. According to the sense of the word “день”(day), it is used in day time.
Добрый вечер means “Good evening”, it is used in the same cases as “Добрый день”, but according to the sense of “вечер”(evening), it is used in evening time.