Remove the joints from the door. Cut about 6 inches off the side of the door with the circular saw where the handles were so there won't be any holes in the surface of the table.
Sand the surface of the door with the sander and the grit paper. If the door was painted sand it until you have a clear wood surface.
Sand the edges of the door with the sander and the grit paper.
Wipe the surface of the door with a dry cloth. Apply the varnish with a brush and wait until it dries. Wear a face mask during the process.
Mark the table where you will screw the table legs on. Screw the table legs onto the door. You can get table legs in most furniture shops. Follow the manufacturer's safety guidelines. The table is ready.