"How do you do" is an old way of saying, "Nice to meet you." No one says that anymore. One thing non-Americans find confusing/funny is the fact that mostly when we say, "How are you," we don't really want to hear how you are. You'll basically get a one word answer, "Fine" or "OK". How are you is mainly a greeting to us, it's not an open invitation to tell us your life story, unless you're friends. "Good night" is something you say when you are going to bed or getting off the phone or leaving for the night. Some slang greetings are "What's going on," or "What's up" or "How's it going".