Are you using Deluxe or Pro? There are a lot more textures in Deluxe so I'm hoping you have Deluxe. Textures can also be found on the net, some are free and others are paid for, you might find something there.
The first thing you will need are some cover surfaces. I added some lines forming triangles along the edge of the boards to complete the polygon. Use the Cover Surface tool to make the six surfaces.
Open the Render Library and select a texture. Apply the texture to one surface. In the Inspector Object Properties click on the render tab then the Advanced button. On the right side of the palette in the preview dropdown select "Drawing" then "update", the selected surface should render. You can make adjustments here such as scale, a little bit goes a long way here so just make small adjustments. Changing the texture can be made in the "Value" box, just update after every change. When you are happy click on "Ok".
Select the "Eye Dropper" tool and tap the "Option" key, set the tool for "Render Material" only, uncheck the other options. Click on the surface you just set up, this loads the Eye Dropper, now hold down the shift key and click on another surface, release the shift key, hold down the shift key and click on the next surface, release shift key and repeat for each remaining surface. The top board is a solid so the texture will be applied on all the surfaces. To remove the texture from the top, in the render library select the upper icon on the right side. This icon is for applying a texture to one side instead of all around. In this case, we are going to remove a texture from one side, grab the "NO" circle and drag it to the top of the board to remove the texture there. Render the project and see how it looks.
If you get stuck somewhere let me know and we will work it out.