Quick answer
pues
Natural: well… / so…
Literal: “then / well”
How it is used
Pues no sé.Well, I do not know.
Pues claro.Well, obviously.
Pues nada, hasta mañana.Anyway, see you tomorrow.
Pues yo creo que sí.Well, I think so.
Where it is said
Mexico is famous for it, often shortened to <b>pos</b> in casual speech, and in Spain <b>pues nada</b> is a standard way to close a chat.
A mini dialogue
— ¿Y qué vas a hacer?— So what are you going to do?
— Pues todavía no lo tengo claro.— Well, I am still not sure.
Watch out
pues
Learners overload it in writing, where it looks sloppy; keep it for speech and for connecting spoken thoughts.
Check yourself
Which sentence best closes a conversation?