Step 2: Using the template with a flush trim router bit
To use the template to make an exact copy of the curved seat, you'll need a flush trim router bit. Because these pieces are narrow, it is easiest to use a router table, however, it can also be accomplished with a hand-held router. Take your template and draw the outline on a piece of wood. In this case, I'm using 3/4" birch plywood. Cut the shape out with a bandsaw or jigsaw about 1/16-1/8" outside the line. The end result is a rough cut piece slightly bigger than the template which will be trimmed smooth using a router. Double sided carpet tape is sufficient to hold the two pieces of wood together for trimming.
A flush trim router bit has a guide bearing which is exactly even with the cutline of the knives (pic 2). The height of the bit is set so that the bearing follows the edge of the template as the blades trim the other piece of wood. The end result is an exact copy of your template. When the trimming is complete, the 2 pieces of wood are simply pried apart and the carpet tape removed (pic 3).