Yahoo was about organizing web sites in an easy to use hierarchical structure, not about searching. If you wanted to learn about "python" the programming language, you'd click computers->programming languages->Python and get a nice list of vetted sites about python. If you wanted to learn about python snakes, you'd click animals->reptiles->snakes->pythons and get another list of vetted sites about snakes. And back in the days when the web was small and search sucked, this was a great way to find sites. Yahoo has been floundering ever since the web grew too big for this approach to be practical, and Alta Vista worked out how to make search work.