Cut the crown molding to length; the bottom of the molding should be the same measurement as the column width. Miter the ends at 45 degrees. Keep in mind that the crown molding must be flipped over when it is being mitered (pretend the base of the saw represents the ceiling). Glue and nail the crown molding to the top of the box column.
Cut the base molding; the top of the molding should be the same width as the column. Miiter the ends of the molding at 45 degrees. Glue and nail the base molding to the bottom of the box column.
Fill the nail holes with wood putty. Sand and stain the column.