how to pass model position of a pixel?

Hello Forum,

i am trying to follow a tutorial about shaders and it says something about the model position of a pixel with a varying vector.

the code used is:
varying vec3 vPosition;
void main() {    
vPosition = position;
gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );
}
this gives me errors in the shader and it doesnt compile...

i am sorry i am really a noob about those things.
what is the right approach within jitter?
thanks for your help