Determine the angle of the miter cut. For example, if you want the wood pieces to fit together at a 90-degree angle, you must miter the edge of each piece at a 45-degree angle.
Place a protractor on the wood section and mark the angle. Draw a line between the marks using a ruler as a guide.
Clamp the wood to a work table with C-clamps so that the area you will cut hangs over the edge of the table. Line up a metal straightedge with the cut line and clamp the straightedge to the wood.
Set the router bit to the depth of the wood. Turn on the router and cut along the line, using the metal straightedge as a guide.