When you meet people greet them saying Good morning/afternoon/evening. This is formal. In an informal style say Hello or Hi.
Good morning is used before 12 pm. In most people’s speech, afternoon starts after lunch and changes to evening after normal working hours.
Evening changes to night more or less at bedtime. But note that ‘Good evening’ usually has the sense of ‘Hello’ and ‘Good night’ or ‘Goodbye’. Good night is not used to greet people.
Common forms of leave taking are given below.
See you. (Informal)
See you later. (Informal)
See you tomorrow/next week. (Informal)
Take care. (Informal)
It was nice to meet you.
A piece of conversation is given below.
John: Good evening. Terrible weather, isn’t it?
Peter: Yes, dreadful.
John: Hasn’t stopped raining for days. Well, I must be going. Good night.
Peter: Good night.