How to say “hello” in English.

Greetings:
To greet someone is one of the most common gestures that people use daily. In the English language, there are several forms of greeting. Depending on the social situation greetings can be formal or informal.
English speaking people use the formal way in situations such as: greeting someone older than you, at work, or greeting a strangerThe formal greetings in English are: “Hello”, “How are you?”, “Good morning, “Good afternoon!” and “Good evening”.

 Informal greetings in English are usually with friends and family in casual situations.
The most popular informal greetings include: “Hi!”, “Hey”, “What’s up”, “How’s it going?” “What’s going on?” “What’s new?”, “What have you been up to?”, “How are ya?”
“Hi” and “Hey” are used instead of “Hello” and expressions such as “what’s up” and “How is it going”… are the informal ways of asking: “How are you?” Normally these questions can be answered with “good” or “not bad….how about you?”

The younger generation (American teens-20s) commonly use “yo”, “Hiya”, “sup” “whatddup?”  “what’s happening?” … with friends (not common in England)

Did you know that the popular mobile phone app called “What’s app?” comes from this informal way of greeting “what’s up?”

source audio: http://english-tonight.com/25-different-ways-to-greet-someone-in-english/