Mark the 2x4s with a speed square or combination square. Then carefully cut the boards to length. If you plan to stain or paint the bench, now is the time to sand the parts. And to really simplify ...

You just need a solid basic plan and a few tools ... Note: Don't cut the drawer fronts until after the workbench carcass is assembled. Cut the 2x4s that make up the top and bottom frames (F and G).