How do I develop ios,android,windows phone app using single code from visual studio

You can't do it just in VS.

You can build a Single Page Application (SPA).

An SPA is a HTML/Javascript application which is a single HTML page with a large Javascript library for providing the applications logic.

There are tools out their which make this approach more manageable and maintainable.

I'd suggest looking at AngularJS and TypeScript

You can then use a transportable SPA hosting framework such as PhoneGap/Cordova.

Once you've finished you development/testing within VS. You use PhoneGap to provide native wrappers within which you embed your SPA. The native wrapper provides a native browser view port which is used to load and present your SPA on the specific mobile device.

Access to phone hardware features is provide through Plug-ins which standardise the API exposed to Javascript. This means your SPA can be a single stream across all platforms as the plugin is platform specific.

But you still have to go through the process of building the package for each platform.

iOS requires MacOSx, xCode and a subscription to the Apple developer program.
WinPhone requires registration with MS and Visual Studio
Android required registration with Google and the ADT which include Eclipse (All of which requires Java too)