how does <<>> work with stringstream code example

Example: stringstream tutorial

#include <iostream>
#include <vector>
#include <string>
#include <sstream>
using namespace std;
int main() {
   string str("Hello from the dark side");
   string tmp; // A string to store the word on each iteration.
   stringstream str_strm(str);
   vector<string> words; // Create vector to hold our words
   while (str_strm >> tmp) {
      // Provide proper checks here for tmp like if empty
      // Also strip down symbols like !, ., ?, etc.
      // Finally push it.
      words.push_back(tmp);
   }
   for(int i = 0; i<words.size(); i++)
      cout << words[i] << endl;
}