If the game is still tied at the end of regulation, there is a sudden death overtime period; meaning, if a goal is scored during this period, the game is over.
During the NHL regular season, the overtime period is five 5 minutes long with 4 on 4 hockey. If the game is still tied after the overtime period, it results in a shootout.
In NHL playoff hockey, the sudden death overtime periods is twenty 20 minutes long with 5 on 5 hockey. The game will continue until there is a goal scored, there is no shootout.