WebGL is an adaption of the OpenGL ES 2.0 standard to the browser to support multi-application usage. Most browser have implemented the WebGL standard, including Chrome and Firefox. However Internet Explorer didn't support WebGL until IE11.
Like the ES profile of OpenGL, WebGL does not come boxed with standard pixel shaders, or vertex shaders. One must load these into the GPU via WebGL; generally held within a script tag.
The pragmatic method of creating a WebGL context is to use an HTML5 canvase, requesting the WebGL context.