Switch controlled by open/closed circuit
You describe a switch which outputs 12V. That is the first diagram.
However that is very simple so I then assumed you need a switch in one place which gives 12V somewhere further away. That is the second diagram.



For the 12V supply you need a battery or a 12V brick (One of these black boxes which plug into the wall). You have not specified how much current you need to switch. What is connected to the 12V?







From your comment: you want the remote point to switch off when the switch is pressed. The simplest way is to use a different type of relay. This way the relay only takes power as long as you press the switch. 







simulate this circuit &ndash; Schematic created using CircuitLab