Can you explain these shaders?

OpenGL Development
#1

I’m currently trying to learn how to add lights in LWJGL through shaders. Google search bought me these two but I don’t understand them. Can you explain them to me please?

[icode]shader.vert[/icode]


varying vec3 normal;
varying vec3 vertex;

void main(void)  
{     
   vertex = vec3(gl_ModelViewMatrix * gl_Vertex);
   normal = normalize(gl_NormalMatrix * gl_Normal);
   gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;  
}

[icode]shader.frag[/icode]


varying vec3 normal;
varying vec3 vertex;

void main (void)  
{  
   vec3 light = normalize(gl_LightSource[0].position.xyz - vertex);   
   vec3 eyeCoords = normalize(-vertex);
   vec3 reflection = normalize(-reflect(light, normal));  
 
   //calculate Ambient Term:  
   vec4 ambientTerm = gl_FrontLightProduct[0].ambient;    

   //calculate Diffuse Term:  
   vec4 diffuseTerm = gl_FrontLightProduct[0].diffuse * max(dot(normal, light), 0.0);
   diffuseTerm = clamp(diffuseTerm, 0.0, 1.0);     
   
   // calculate Specular Term:
   vec4 specularTerm = gl_FrontLightProduct[0].specular * pow(max(dot(reflection, eyeCoords),0.0), 0.3 * gl_FrontMaterial.shininess);
   specularTerm = clamp(specularTerm, 0.0, 1.0); 
   
   // write Total Color:  
   gl_FragColor = gl_FrontLightModelProduct.sceneColor + ambientTerm + diffuseTerm + specularTerm;     
}

The main problem in them is the terms and how they works.