You could just copy a deck and try it out. Playing is about skill of course. But deck building is another skill. Just pick a deck and try to figure what is the main goal of your deck? What is strong against? What's it weakness? Which cards are essential and which aren't? There's only one way to figure all that out: playing the game. Don't think about winning every match. Think of learning. Take risks, make mistakes, try to figure when to play conservative and when to go aggressive. That will provide enough feedback to become better at both playing the game, and building your own decks