To say goodbye we use many different expressions. Adiós is the most common. It is easy if you remember that it means “a = to” and “Dios = God”, “to God”, which is a summary version of “I entrust you to God“. Curious, uh?
“Hasta luego” is also very common. It is difficult to translate it. In English, “see you later” is used, but in Spanish we use the word “hasta”, which literally means “until”, it is like saying: “I will not see you more until later”.