If you want to add a touch of rustic charm to your home, consider finishing your plywood walls with a natural stain. This will give the wood a warm, inviting look, perfect for any room in the house. First, you must sand the plywood walls to create a smooth surface. Then, apply a generous amount of stain to the walls using a brush or rag. Be sure to work the stain into all of the cracks and crevices for complete coverage. Once the stain has been applied, allow it to dry completely. Then, apply a clear sealant to protect the wood and prevent the stain from fading.