"Nice to meet you."
Memnun oldum is just short for Tanıştığımıza memnun oldum. Tanıştığımız means "our meeting" or "our becoming aquainted". You can leave it out because it's clear why you are pleased. In French and Spanish you can just say Enchanté(e) or Encantada/o. It's a fixed phrase with a clear contextual meaning. You can say the full sentence if you can be bothered.