When the batsman (1) calls Yes the coach rolls the ball towards the fielder stood by the stumps.
Fielder (1) runs across, picks up the ball and then tries to run out the batsmen.
Repeat with the next fielder and batsman.
Each batting team has a certain number of wickets (eg. 3 wickets). The teams change over once the batting side have lost all their wickets.
Ultimately the coach here decides how hard this drill is for their team - the faster you roll the ball the faster the players need to run.
The batting side must complete their runs with their bat in hand.