GLSL tutorial 3 - vertex and fragment shader

//http://www.youtube.com/user/thecplusplusguy
//vertexshader, create a file for it as vertex.vs
#version 120
uniform vec3 color;
varying vec3 color2;    //out
attribute vec3 atr; //in
varying vec2 texcoord;

void main()
{
    gl_Position=gl_ModelViewProjectionMatrix*gl_Vertex;
    color2=atr;
    texcoord=gl_MultiTexCoord0.xy;
}

//fragment shader, create a file for it named fragment.frag
#version 120
uniform sampler2D img;
uniform sampler2D img2;
uniform vec3 color;
varying vec3 color2;    //in
varying vec2 texcoord;

void main()
{
    vec4 texcolor=texture2D(img,texcoord);
    vec4 texcolor2=texture2D(img2,texcoord);
    gl_FragColor=texcolor2*0.5 + texcolor*0.5;
}