WoW Classic is available on Battle.net for those who have an active subscription to World of Warcraft. It's just a different download on the application. 🙂
But!! If you don't want to subscribe to it, I can recommend the private server called: Project Ascension. It's absolutely amazing. And VERY populated.
It's also very easy to get into. You just sign up and download the client and log in. It's also free. 🙂
Yay!!!!