I used to play high school soccer 63 years ago so I need an answer?

Basically the clock doesn't stop during injuries or free kicks and other stoppage's, so the referee estimates the amount of time the game has been stopped for and then adds it on at the end, he can add on however much he thinks is necessary and then that's a minimum additional time that must be played

It's a bad system actually that's far behind other sports that just pause the clock but it also adds excitement into the game and gives fans hope for an extra time goal as they know the whistle won't be blown on exactly 90 minutes

The game has to be 45 minute halves (90 minutes). If there is an injury or stoppage of play the referee will stop time on his watch and add it on so 45 minutes are played in each half.

Clock keeps running but the referee can add time for Injury, subs, and general time wasting to the end of the half as he sees fit. what used to be secconds, over the years it has become a lot of time averaging somewhere arround 4 mins per half, almost 10% of the total game time