Windows: begin by selecting GedScape from the Windows Start menu, or from an icon on your desktop. Mac: begin by opening the GedScape icon from your Applications folder or from Launchpad.
Choose File|Open (i.e., select the Open option on the File menu).
GedScape also has a built in GEDCOM file for demonstration purposes. To display this, choose File|Open Sample GEDCOM.
NOTE: With the Windows version you can also right-click over a GEDCOM file icon in Windows Explorer, then select GedScape from the Open With menu. And once the program is running you can drop a GEDCOM file icon from File Manager (Mac: use the Finder) onto the GedScape main window to display the file.