Shader

[NouCake]

Hey guys,

I'm very new to shaders so I know nothing, not even what to ask google.

I could grab this piece of code together from examples but I'm very confused with everything.
I don't even know which language this is

precision mediump float;
varying vec2       vTextureCoord;
varying vec4       vColor;
uniform sampler2D  uSampler;

void main( void ) {
    gl_FragColor = texture2D(uSampler, vTextureCoord);
    gl_FragColor.rgb = vec3(gl_FragColor.r, gl_FragColor.g, gl_FragColor.b);
}

Where does vTextureCoord, vColor come from? Can i pass my own data into the shader/how?

Can someone send a link where i can learn more about this or the documentation for which terms i can pass into it like vTextureCoord.

Thanks alot