The syntax for the config files is quite easy. Basically, you tell CWallpaper which wallpaper setting program to use, and which options to use for what. The config cwallpaper runs when it starts without options is saved as

An example config file:
program: fbsetbg
scale: -a
center: -c
tile: -t
default: s

This config file would tell CWallpaper to use the program fbsetbg to set the wallpaper. It also says to attach a -a to the end of the command when the user selects the scale to fit option. It will attach a -c to the command to center the image, and a -t to tile it. The default option tells it that the default option is scaling to fit.