The above is a picture of the mains tap, if you know what it is and yours works fine then you don't need to read any further. However if you are like some people who have never turned the mains tap the chances are is that it has seized up.
These taps are prone to seizing up. So whether you are a house owner or living in rented property you must know where this tap is located and it is fully working because if you get a water leak or burst pipe.... this mains tap is the only thing which will help you before a plumber can arrive.