Vegas Dream contains four gambling mini-games: Blackjack, Roulette, Slots and Keno. The goal is to raise as much money as possible at any one of these events; the player can create a persistent profile that carries over cash between each mini-game, so there's no penalty for switching.
There are also certain events that occur while the player is gambling. These can include NPCs asking the player for money, or a particularly wealthy individual that challenges the player at a single game of the NPC's choosing. Usually, the results of these events have an equal chance to end in, or against, the player's favor, much like the gambling games themselves.
Blackjack, roulette and slot machines are all commonly known venues for gambling. Keno is a bingo/lottery game where numbers are called out and payouts are based on how many of those numbers each punter correctly predicted would appear.