Hey world! Leap second isn’t a new thing. Don’t worry.
A leap second is the adjustment of one second to the current time to coordinate it with universal time in order to keep its time of day close to the mean solar time, or UT1. Without such a correction, time reckoned by Earth’s rotation drifts away from atomic time because of irregularities in the Earth’s rate of rotation. It is not the first event because it has happened in past.