To edit a path rule double click on the name of the rule, this will open the rule options. To disable or enable path rules click the checkbox to the left of the path rule name. By default all the path rules will be enabled.
The default rule set will have been installed by the 'AvidCNC for SheetCam' installer. The Path Rules window will then be displayed.
To open the cutting rules editor press the Cut Rules button on the left of the Tools menu on the left of the SheetCam application window, or use the drop down menu Tools -> Cutting Rules.