Extra time in soccer is implemented during the knockout stages of the FIFA World Cup when a match ends in a draw after the standard 90 minutes of regulation play. The purpose of extra time is to determine a winner without the match concluding in a tie.

Extra time consists of two halves, each lasting 15 minutes, for a total of 30 additional minutes. The game continues in full, with teams switching ends after the first 15-minute period. If a winner is not decided by the end of the 30 minutes, the match proceeds to a penalty shootout.

This format is used exclusively in knockout rounds, where a decisive outcome is required. Group stage matches, in contrast, can end in draws without advancing to extra time.

Sources: https://www.foxsports.com/stories/soccer/world-cup-extra-time-rules-what-extra-time-how-does-work