Formal:
* こんにちは (Konnichiwa): This is the most common and polite way to say hello. It's appropriate for most situations.
* おはようございます (Ohayou gozaimasu): This is used to say "good morning". It's more formal than "おはよう (Ohayou)" which is more casual.
Informal:
* こんにちは (Konnichiwa): This is also used informally, but it's less common than "Konnichiwa".
* おはよう (Ohayou): This is a more casual way to say "good morning".
* こんばんは (Konbanwa): This is used to say "good evening".
* もしもし (Moshi moshi): This is used to answer the phone.
Other greetings:
* 初めまして (Hajimemashite): This is used to say "nice to meet you" when you're meeting someone for the first time.
* 久しぶり (Hisashiburi): This is used to say "long time no see".
Choosing the appropriate greeting depends on the situation and the person you are speaking to.