Shut Off Water and Drain Tank

What happens here

Before starting any work inside the toilet tank, turn off the water supply. Locate the shut-off valve on the wall near the base of the toilet and turn it clockwise until it's completely closed. Place a sponge directly below the supply line connection to the toilet tank to catch any drips. Flush the toilet to drain most of the water from the tank. Then, use the sponge to absorb any remaining water in the tank. Disconnect the flexible supply line from the threaded connection at the bottom of the old fill valve by unscrewing the nut.

Goal: Prepare the toilet for fill valve replacement by stopping water flow and emptying the tank.