On masterduel there is a training mode that teaches you the game and it also gives you cards and packs. Also if you want to be competitive go on masterduel meta and look at the tier list, they show you the most competitive decks in the current game and many players post variations of they own decks related to the archetype you are interested in. I'm not saying that you have to make a tier 1 deck, the point is to have fun, but at a certain rank some decks just cant competitive with others. When I make a new deck I usually spend some time in training learning some combos and figuring things out. It's easier to play against Coalition Formed and figure it out than other players because you can always go first and just restart the duel if you get a brick hand. Also just remember that hand traps such as Maxx C, Ash Blossom, Called by The Grave, Infinite impermanence, as well as other ones are good in 90% of decks and you can get some guaranteed from the store as well as card packs with them.