First meet someone
"你好" means "Hello", sometimes it can be consider as "Nice to meet you". When first meet someone,Chinese native speakers usually speak in this word and used in most other senses. And 您好 is a more formal way.
Generally, people use kinds of words or phrases with features to ask for another when they are in a good relationship, such as "你吃了吗?". Those words are like what was used in English such as "how are you?" and "how is going?"