Make a simple wooden texture in The Gimp

Step 4 Make it bumpy

Next, you need to duplicate the layer, desaturate the duplicate, and use it as a bump map to the color version. This step descrbes these actions and how to do them, advaced users can do this quickly and skip to step 5. But for all you novices, listen up!

Duplicate the layer: Layer -> Duplicate layer.

Desaturate the duplicate: Layer -> Colors -> Desaturate

Bump map: First, select the original layer. Dialogs -> layers, click on the colored layer. Then, use the desaturated layer as a bump map Filters -> map -> bump map...

Now, all you need to do is delete the desaturated layer. Using the layer dialog select the B&W layer and delet it by pressing the trash can button.