Skill-capped offers help in the form of videos and the like, I'm guessing it's good for starter knowledge but you can do that by watching some streamers on twitch anyways.
My advice to you is, don't try to run before you can walk tbh, many people here are trying to give you good advice but I think most of these advice are a lot to handle for your present situation.
If I were to give you some advice myself, I'd say start by checking out what every single class can do, go on wowhead and look through all class talents/specs and see what they get, including passives etc. The saying "knowledge is power" is not a joke tbh, to win you need to understand what is going on and how classes react, you gotta start somewhere.
After that I'd say go and duel every single class you can , do it over and over regardless of how good they are, doing this will help you improve your class vs class knowledge , understanding how a single class works completely before moving on to how classes work together.
After that you can follow the above advice and start watching some streams to follow up on the learning curve, but I must tell you, there is a tremendous amount of information you'll be going through to get there. GL : >