It's a very common and informal greeting, similar to "Hi" or "Hey" in English.
Here are some other ways to say "hello" in Italian, depending on the context:
* Buongiorno: Good morning (formal)
* Buonasera: Good evening (formal)
* Buona sera: Good evening (informal)
* Buon pomeriggio: Good afternoon
* Salve: Hello (formal)
* Giorno: Hello (informal, used mostly in the south)
The best choice will depend on the situation and your relationship with the person you're greeting.