All branches of the explorer tree except the last one (Drawings) enable you to set parameters for the program as a whole.

Files

This branch acts just like Windows Explorer. The files that are listed for a highlighted folder depend on what Filters are set. You can list all files, only DoubleCAD files, only image files, or you can define your own filter for files of specific extensions.

You can expand a folder by clicking the "+" icon, or by pressing the * on the numeric keypad.
If you highlight a DoubleCAD file (*.2cd) or an image file, a preview of the file will appear.

Program Defaults

Here you can control default program settings - parameters that are active for all files. For example, you can change the aperture size and toggle Auto Add Constraints on and off. Most of these parameters can also be set in Options / Program Setup.

Symbol Libraries

Enables you to change the path for user-defined symbols. You can also drag symbols as you would from the Library palette.

See Library Folders.