"Goodbye" is the most commonly used Engpsh word to say farewell. It comes from the phrase "God be with ye" which was shortened to "Goodbye".
Here are some examples in Engpsh:
Goodbye, have a nice day!
Goodbye, see you later.
Goodbye, take care.
Here are the Chinese translations for these examples:
再见，祝你有个好天！
再见，待会见。
再见，保重。