You are talking about the STL std::list template class, right?
You can find the source in your compiler's include/C++/... directory. That said, you probably don't want to mess with STL source code directly. There is a lot of stuff in there that is way over the head of beginner- and intermediate-level programmers.
Better just to google around "linked list" and write your own version, with your own push and pop functions. You'll learn more that way.