The custom code entry dialog is shown when clicking on the  add button in the Custom Code & Resources tab.

The following entry types are available:

•  Class or resource files
  For simple actions, screens or form components that do not depend on other classes, it is easiest to insert their class files directly, especially if you build your installer extensions together with your application. Anonymous inner classes will be included automatically. If you select a resource file, e.g. an image, it will be added to the top-level directory of the custom JAR file and will be available via Class.getResourceAsStream().
•  Directories
  With this type of entry you can add an entire directory. Please make sure to select a classpath root directory, otherwise your classes cannot be loaded.
•  Scan Directories
  With this type of entry you can add all JAR and ZIP files in a selected directory.
•  Archives
  With this type of entry you can add a JAR file. JAR files can optionally ne mapped to installed JAR files, so that they are not duplicated if they are used by both custom code and launchers. Please see the help on the Custom Code & Resources tab for more information.

Use the ... chooser button to select files and directories from your file system. A relative path will be interpreted relative to the project file.