If I'm not mistaken, you mean "au revoir" and "à bientôt". There's no radical difference in meaning, but "au revoir" is more like "good bye" and literally means "till seeing again" or "until I see you again/we see each other again". " A bientôt" is equivalent to "See you!" or "See you soon!" in English. Literally it means "till soon.".

MERIC MORPHEUS