The red zone appears periodically on the PUBG map, regardless of which map a player chooses. Within its 1 kilometer range, indicated on the map by a red circle, players run the risk of being hit by a random explosion.
The zone itself is chosen randomly and automatically, as are the bombing locations. If a player is hit by one of the explosions, that player will be killed instantly.
The surest way to survive the red zone is to avoid entering at all. If it appears on top of you, simply stay inside until it moves away.