Here's an explanation of NHL overtime rules, including the difference between the regular season and playoffs.
When National League Hockey games have a tied score at the end of regulation, they go into "overtime" to determine a winner—both in the regular season and playoffs.
Each team receives one point in the league standings for going into overtime.
In the regular season, the teams play one five–minute overtime period with the first team that scores being the winner. The winning team receives an additional point in the standings.
The overtime period has three skaters and one goalkeeper. If a team decides to pull their goaltender in the overtime period in favor of an extra attacker and lose the game, they forfeit the automatic point gained when the score was tied at the end of regulation.
If the game remains tied at the end of a regular season overtime, the game goes to a shootout, with each team given three shots. if the score remains tied, the shootout will go to a "sudden death" format.
A team can decline to participate in a shootout, and if they do, they will be given a shootout loss.
In the Stanley Cup Playoffs, teams tied at the end of regulation play 20 minute periods, with five skaters each. The first team that scores is declared the winner. Essentially, the game is just extended as normal until someone scores. There are no shootouts in the playoffs.