Instructions
Consult the game's manual. Each game in the 5Ds series comes with a manual that explains many of the game's basic concepts, such as controls or specific card types. This can be a great place to go when you need a refresher on the overall mechanics of the game.
Read a walk-through or game guide. These materials are typically available online for free and provide a step-by-step explanation on how to complete the game it is written for. Many of the games in the 5D series have multiple walk-throughs and game guides for you to choose from. Because an official game guide has never been created for games in the series, these are ideal for many players.
Consult Konami's support site, particularly if you are having technical problems. Konami owns the rights to the 5D series, and it has a team of employees dedicated to assisting players with errors on their game. They aren't there to help you get past a difficult part of the game, but they will gladly assist you in fixing any errors your game may have.