Formal:
* Olá: This is the most common and polite way to greet someone, similar to "hello" in English.
* Bom dia: Good morning (used until noon)
* Boa tarde: Good afternoon (used from noon until evening)
* Boa noite: Good evening/good night (used from evening onwards)
Informal:
* Oi: This is a more casual and friendly greeting, similar to "hey" in English.
* E aí? This is a very informal and friendly greeting, often used among friends. It translates literally to "And what about you?"
Other greetings:
* Tudo bem? This means "How are you?" and is a common way to greet someone, especially in informal settings.
* Tudo bom? This is another informal way to ask "How are you?"
The best way to choose the right greeting is to consider the situation and your relationship with the person you are greeting.