Cut the 4-inch by 4-inch piece of lumber into six equal sections. Each section measures 2 feet in length. These are the legs for your bench.
Set up four of the legs in a rectangular pattern. Set the plank on top of the legs. Adjust the legs so that they are flush with each corner of the plank and there is no overhang.
Screw the legs into place. Use at least two screws per leg for maximum stability. Measure the distance between the legs on the long edge of the plank. Set the remaining two legs in the middle of this measurement. Ensure that the edge of the leg is flush with the edge of the bench. Screw these into place as well.
Cover the screw heads with the wood putty. Using the putty knife, fill the indentation in the wood with the putty. Scrape away any excess putty. Wait for the putty to dry before painting or staining the bench.
Prime and paint the bench or stain it, as you prefer. If you do decide to paint the bench, make sure to prime it first. Unprimed wood soaks up paint unevenly, and your finish may end up looking blotchy. Let finish dry before using the bench.