Its probably best for you to watch some youtube videos or read up on basics about loops. Anyways, here is a very simple way to understand this
#include <iostream>
int main(){
char choice="Y";
//enter this loop since 'choice' equals Y
while(choice == 'Y'){
//run the game
//if they enter anything else other than Y, it will stop the loop
std::cout << "Would you like to play again (Y for yes, N for no)? \n";
std::cin >> choice;
}
return 0;
}