Greeting: ni hao! (Hello!)

"ni hao" (nǐ hǎo)  is one of the most common greeting in China.
Its usage is similar to "Hello" in English.

You can also say: "ni hao ma?"
Literally it means "Are you fine?"
It is similar to "How are you?" in English.

Example:

[Chinese]
Mr. Wang:  nǐ hǎo ma?
Ms. Chen:  wǒ hěn hǎo!

[English]
Mr. Want: How are you?
Ms. Chen: I'm fine.

More Information:

You might wonder what's the difference between "chi bao le ma" and "ni hao ma"
Please check:
Difference between "Chi bao le ma" and "Ni hao ma"