Formal:
* Bom dia: Good morning (used from sunrise to noon)
* Boa tarde: Good afternoon (used from noon to sunset)
* Boa noite: Good evening (used from sunset onwards)
Informal:
* Oi: This is the most common and versatile greeting, suitable for friends, family, and acquaintances.
* E aí: This is a slightly more informal version of "Oi," often used among close friends.
* Olá: A more formal "Oi," used for people you don't know well.
Other greetings:
* Tudo bem? (How are you?) - This is a common greeting, especially among friends and family.
* Tudo bom? (Is everything good?) - Another informal greeting, similar to "Tudo bem?".
* Como vai? (How are you?) - A more formal greeting, suitable for people you don't know well.
Remember:
* "Bom dia," "Boa tarde," and "Boa noite" are always used with a person's name when addressing them formally (e.g., "Bom dia, Maria").
* "Oi," "E aí," "Olá" are generally used alone, but can be followed by a person's name in informal settings (e.g., "Oi, João").
Choose the greeting that best fits the situation and your relationship with the person you are addressing.