With a shot clock at the table, players have a certain time to act on their hand. Typically players get 30 seconds per decision. On top of that, in most poker tournaments operating a shot clock, players get a certain amount of time bank cards. These cards are typically worth an additional 30 or 60 seconds.
The shot clock is a physical clock on the table that counts down the time players have left to act on their hand. Once the clock reaches zero without the player having decided to call, fold, bet, or raise, a player's hand is either dead, or a player is forced to play one of their time bank cards to gain some more time to think.
Every tournament organizer decided how many time bank cards players get at the beginning of the tournament. If a player has time bank cards left when he or she busts, those are typically forfeited. Some tournaments let you carry over your time bank cards to coming days, and some give out additional cards upon making the next day, and/or making the final table.
The shot clock told us Phil Ivey only had 3 seconds left to act when he moved all in!