We say “Zdarova!” (“Здорово!”) to our close friends. The stress is on the second syllable in this word. The word is an analog of “Hey!”, “Hi!” or “Hello!”. “Здорово!” is a slang word. It’s an informal friendly greeting. It’s an analog of “What’s up?” or “Sup!” or “Yo!”. It’s basically used among the young mostly by men.
It’s quite a rude word. And you should use it if you greet one person who is your age, not a group of your friends.