Are they traditional Dresden Plates with the curved end blades? If so, you need to turn under the curved edges for sewing them down. You can make a cardboard template the same curve as the blade end and use it on the wrong side of each blade to help press over 1/4 inch with your iron.
If you have done the pointed end Dresden Plate, then it is ready to stitch to a background square. You can either hand appliqué it down or machine appliqué it to the background square. Some people like to stitch the center circle on before stitching the plate down, some people like to stitch the center circle down after the plate is appliquéd to the background square. If you look on Youtube, there is probably a tutorial on Dresden Plates.