"Memnun oldum. Hoşça kalın."
Translation:Nice to meet you. Bye.
Güle güle is said to someone leaving BY THE PERSON STAYING. It means "smilingly/laughingly/happily" and is short for "Güle güle gidin" -- so it's like saying "Go forth from here happily!"
Hoşça kal(ın) is maybe slightly more often said by the person who leaves (not a hard rule, though--can be said on the phone, or when two people part, or even by the person staying). It means "Stay nicely/well."