From the official Digimon website:
The Digimon Card Game is a competitive trading card game. Each player has a companion Digimon in the battle area to attack the opponent. Your Digimon evolves, gets stronger, and gains new power! You win by beating your opponent’s security (reducing your opponent’s Security Area cards to zero) and delivering a knockout blow!
Digimon Tournaments are held at RSG every Friday at 6:30 PM. Official Bandai promos and prize support are available to tournament participants.