Measure the width of the bed, then take the measurement from the floor to the top of the mattress. The finished headboard will need to sit at least 18 inches higher than the bed.
Lay a sheet of paper on the ground, and draw a rectangle with the same width measurement as the bed. The length of the rectangle should be the measurement from the floor to the top of the mattress. Fold the paper in half lengthwise. Draw a curved line from the top centerpoint at least 18 inches away from the rectangle to each top corner of the rectangle to make the curved top of the headboard. Cut out the template.
Tape the template to a sheet of plywood and draw its outline with a marker. Cut the shape out with a jigsaw, and sand the edges to smooth them.
Lay the batting out on the floor, and place the wooden headboard on top. Cut the batting roughly around the headboard leaving an allowance of 2 inches. Fold the batting over behind the board and staple it into place with a staple gun.
Lay the horse-motif fabric on the floor, right side down. Lay the headboard on the fabric, batting-covered side down. Cut around the fabric leaving a 3-inch allowance, and fold the fabric around the headboard. Staple into place.
Have an assistant hold the headboard against the wall. Make a mark on the wall to show where each edge of the headboard comes to. Measure and mark on the wall 2 inches in and up from each bottom corner of the headboard. Drill two holes in the wall and put in an anchor.
Measure and mark 4 inches up from each screw hole, and drill two more holes. Put in anchors. Measure, mark and drill four corresponding holes in the headboard. Have your assistant hold the headboard in place while you screw it to the wall.