When setting up permissions for your group and assigning which modules that group can access, you have the ability to filter using a custom rule.
To use this feature go to Admin> Group and click on the desired group heading then click Permissions. Select the module by either activating Access or Create permissions.
From the Add menu select which custom rules you would like applied.
Additionally click Details. This will display custom rules for content where you can select the access level for each of your resources (including any sub folder, just click on the arrow to expand the selection).
If you do not want a group to access a specific resource do not select any of the 4 options.
* Note that the name given to modules, features and information items may vary in your platform as they can be customised by Main Admin users.