Place a portable power miter saw on the workbench. If the portable saw features built-in clamps, clamp the saw to the table to prevent it from shifting while in operation. If the saw does not feature built-in clamps, tighten a C-clamp over the base and under the edge of the table on each side.
Measure the length of the wall with a measuring tape. Mark the measurement on the molding.
Adjust the power miter saw blade to a 45-degree angle and tighten the adjustment knob. When cutting an inside corner, place the molding with the back facing the back of the saw. When cutting an outside corner, the front of the molding should face the back of the saw.
Stand the molding section under the saw blade against the guard. Turn on the saw and cut through the molding with a slow, even motion. Repeat this process to cut additional molding sections.