not a tut, but you can try in the tut section of the board
basically, you have your geomettry (model) and all a shader is, is something which gives your model a colour, or a texture if you will eg. you model a box, you apply a brick type shader (which is just a simple image file) and it looks like a brick wall
but using a simple image file wouldnt be enough as that would just give your wall a colour, you would need to create a bump map, which makes the bricks on the wall stand out, and the cement stick inwards

all of this put together, everything thats added to the model to give it a texture, is called a shader

hope i havent confused you, its half 2 in the morning sorry