Informal:
* 你好 (nǐ hǎo): This is the most common and versatile way to say "hello" or "hi" in Mandarin. It's appropriate for most situations, both formal and informal.
* 嗨 (hāi): This is a more casual and friendly way to say "hi". It's often used among friends and family.
* 哈喽 (hā lōu): This is a more modern and informal way to say "hi". It's often used by younger people.
Formal:
* 您好 (nín hǎo): This is a more formal and respectful way to say "hello" or "hi". It's used when addressing someone older than you, someone in a position of authority, or someone you don't know well.
Other:
* 早上好 (zǎo shang hǎo): This means "good morning" and is used in the morning.
* 下午好 (xià wǔ hǎo): This means "good afternoon" and is used in the afternoon.
* 晚上好 (wǎn shàng hǎo): This means "good evening" and is used in the evening.
It's always a good idea to listen to how native speakers use these greetings and to observe the context in which they are used.