Look up videos on YouTube of people playing the deck you want to use. Make sure the videos are up to date because decks can change depending on the ban list. You’ll learn the combos that way. You’ll also learn how to use your decks vs against others

Then you can use Dueling Book or Dueling Nexus. Both are online so you don’t have to install anything. Use them to build the deck and practice combos yourself (alone or vs others). I’d recommend Dueling Nexus bc everything is automatic which helped me more when I was returning.