The best thing you can do to learn how to host games is to dive in and just start with one you like. I enjoyed running one on a spare computer while I was in college and learned a lot about computers in the process. All games handle differently than each other, even ones that share the same engine. Mods/add-ons/etc. throw in another X factor.
Because all games are so different, you probably won't find a single site that acts as a tutorial for all of them. Especially not for something like WoW, which I think is technically not authorized to run privately.