You'll start by building your deck, choosing from a massive library of cards. Then, you'll jump into duels against the AI or other players online. The goal is simple: reduce your opponent's life points to zero before they do the same to you.
As you play, you'll unlock new cards, characters, and other goodies. It's amazing how much depth and complexity there is - you'll be discovering new strategies and combos for hours on end. The more you play, the more you'll want to play!