There are many polite phrases you have to get accustomed to - "nice to meet you" is one of them.
After you meet someone for the first time and you are parting ways, you say the required phrase.
At work, we have a reporter who insists on saying "nice to meet you" after she gets off the phone with people. It drives me crazy! After a long interview for a feature story, she'll say "Ok, it was very nice to meet you!" before hanging up.
I cringe in my seat across the room.
"You didn't meet them!" I want to yell out. "You just talked to them on the phone! It is NOT the same thing!!!"