This is usually found under your kitchen sink. Turn clockwise to close and anti clockwise to open.
Isolation Valve – Used to turn off water to a single appliance ( Tap, Toilet, Washing Machine…)
Use a flat screwdriver or a bread knife to turn the screw head horizontal to turn off and vertical to turn on. On some valves you can use your hand.
Toilet not flushing?
Use a bucket of water to throw down the pan to manually flush the toilet until your find a plumber to repair.