Help with adding image to model

I have made a model and I want to add the texture of the image to it, I have a metal image and want to apply it to the box (image of model box below) to make it look more si fi, any help?

(so in basic terms add a image to the whole box)

Any help???

first setup uv mapping
open another window for image editing uv
now on your model in edit mode type u and unwrap bring image in to image uv editor and place all the verts where you want
one done go to materials and add texture image select that image and choose mapping uv