The verb giocare means "to play," in the sense of playing a game or a sport. When referring to sports, it is usually followed by the Italian preposition a:
I bambini giocano sull spiaggia. (The children play on the beach.)
Mario e Carlo giocano a carte. (Mario and Carlo play cards.)
Paola gioca molto bene a tennis. (Paola plays tennis very well.)
The phrase giocare d'azzardo means "to gamble":
Pietro gioca d'azzardo e perde sempre. (Pietro gambles and always loses.)