How to say hello

Hi everybody,this is my second entry.You may think it is boring on the title.Nomatter how you think,there are rules to say hello.If you see your old friends "hi","hey" or anything,it's ok.But if you see a sir or a madam you should say "hello sir/madam", to be polite.There are many ways to greet each person to another.Well but i don't know very well about them.It is just an example. Ok? Have a nice day!!!