Fusible web (sold as Stitch Witchery, Heat N Bond and other trade names) melts to adhere the fabrics together. Fusible web may be available in various weights. Although it may seem like a heavy bond will adhere better, it is not advisable if you will be sewing the edges. Heavy bond will also be stiff after it is melted. Light weight bond is preferable when doing applique.
To be sure that the fusible web will adhere to the fabrics, wash the fabric before starting the fusing process. Always read instructions that come with the fusible web.
Once the process to adhere the fabrics is achieved, the raw edges of the applique must be protected or enclosed if the item is going to be laundered. Fabric paint or machine stitching are the most commonly used method to protect the edges of the applique.