To say hello/how are you?, you have different possibilities depending on the context:
-Salut! (among friends) (this word can also be used to say "good bye"(-Allez, salut!...and you leave...)
-Bonjour! (neutral, very usual)
-Ça va? (it's like "how are you" in an informal context, very usual)
-Comment allez vous? (it's like "how do you do?", formal)