To open the tap rotate the cap in the anticlockwise diren. Since the threads are right handed the spindle with the valve disc is screwed out of the main body. Clockwise rotation brings the valve disc into the contact with the seat and thus closes the tap.Once the valve disc has left the seat uncovered water oozes out from the seat & thus water flows out as mentioned in the main body component drawing.
When the valve disc covers the seat the water passage stops.