Measure the span between the two sides of the desk with a tape measure held to the inner edge of each side. Write down the height from the bottom edge of the desk to the floor, or as close to the floor as you want to cover with the modesty panel.
Mark the wood with a pencil and tape measure to draw the outline of the modesty panel, which will typically be in the shape of a rectangle. Use a wood variety that matches the desk.
Cut out the modesty panel with a circular saw while wearing safety glasses to protect your eyes from saw dust. Wear a dust mask to avoid inhaling flying wood particles.
Sand the edges of the panel, if desired, with a sheet of sandpaper.
Test fit the modesty panel by holding the piece in the desired position on the desk. Mark the mounting points with a pencil; for example, you may use two brackets on the left edge of the panel and two on the right.
Attach the modesty panel to the inside front of the desk with L-shaped brackets. One end of the bracket connects to the edge of the modesty panel with a screw and the other end of the bracket attaches to the inside wall or support on the desk with a screw.