In poker, going all in means betting your entire stack on a single hand. It’s important to point out that whenever one of the players is faced with a current bet that exceeds the size of his stack, making the call would also be considered going all in.
Furthermore, in such a case the player in question won’t be able to win any money that would exceed the total size of his bet from any participant of the game. Finally, whenever a player does not have enough money or chips to cover the ante and/or the blinds in a hand, that player is always automatically all-in for the coming hand. The money is applied to the ante first – when the entire ante is covered, the remaining funds are used to cover the blind.
Player A has a stack of $300, player B has a stack of $150, while player C has a stack of $500. Player C goes all in, while A and B call. Therefore, the pot equals $150+$300+500 = $950.
Player B ends up winning the hand, but since he didn’t have enough money to cover player C’s bet, he wins $150 from player C and player A. If player A had the second-best hand, he’d win $150 from player C, who’d end up losing $300 in total.
While going all-in is somewhat rare in fixed-limit and pot-limit games, no-limit games are notorious for allowing players to bet their entire stack at any point during the hand. Please note that some brick and mortar casinos might require players in the big blind position to have enough chips to cover the small blind and ante in order to be dealt in – any player that lacks those funds will not be dealt in.