in order to make it smooth you either need to sand it until it, or fill it until it is smooth. After you fill it and sand it then you can prime it with at least 3 coats. then finish paint it and then a polyuerethane with a light sanding between coats and you will have a finish like glass. instead of poly you can also wax it, but poly lasts longer.
for filling look for any paintable wood putty. http://www.lowes.com/lowes/lkn?actio...052&lpage=none