Understanding stringstream

I have never used stringstream before and was given a sample code but with no explanation of what was happening in the code. If someone could explain each line's purpose that would be great. I have looked in multiple places but cant seem to pin down the second line.

#include <sstream> // i know this line includes the file

stringstream    ss(aStringVariable);// this line in particular 

ss >> aVariable;

getline(ss, stringVariable2HoldValue, ‘|’);