Measure the post with a tape measure and mark the length on all four faces with a quick square. Cut the post to length with a circular saw set to its deepest cutting depth. Cut along the line on one face, roll the post over and cut along the line on the opposite face.
Cut two pieces of 1-by-8 hardwood lumber to width on a table saw at 7 inches. Cut these two pieces to length on a miter saw, the same length as your post. Cut two hardwood pieces of 1-by-6 to the same length using the miter saw.
Cut eight pieces of 3/4-inch thick, 6-inch high baseboard molding, in the same wood grain as your hardwood pieces, to length at 8 1/2-inches. Set your miter saw at 45 degrees and stand the baseboard pieces on the saw, with the bottom edge on the saw table and the back against the fence to cut down, through the height of the molding. Cut each end at 45 degrees, one right and one left, so that the face of the molding is longer than the back.
Apply wood glue to one of the faces of the post and fit one of the 1-by-6 hardwood pieces to the face of the post. Nail it in place with a pin nail gun and 1 1/2 inch nails, one every 6 inches. Fit the remaining 1-by-6 to the opposite face of the post in the same way.
Glue and nail the two cut down 1-by-8 pieces to the two remaining faces in the same way, aligning the lone edges with the faces of the 1-by-6 pieces.
Apply wood glue to the back of the molding pieces and nail them to the column, wrapping around all four column faces and matching the mitered corners up. Fit four pieces around each end, with the square bottom edge of the molding facing out to the end of the column.
Fill all seams and nail holes with wood filler. Allow the filler to dry and sand the column with 150-grit sandpaper. Apply two coats of stain and clear finish all-in-one with a soft brush. Work with the grain in long, straight strokes, spreading the finish evenly to prevent drips. Allow the first coat to dry for two to three hours before applying the second coat.