If you have created a desktop shortcut/alias just double click on it to start Really Simple Barcodes. Otherwise, open the folder in which you installed the program and double click on the program file (which is RSBarcodesW.exe for Windows, or RSBarcodesX.app for Mac OS X and RSBarcodesM.bin for Mac OS 9)
When the program opens for the first time it will check for a default printer and display the page layout dialog. (On subsequent startups this dialog will not appear unless you request it by selecting Page Setup from the File menu). If you are opening the program for the first time you can just push the OK button for now, but if you plan to print labels you are advised to select the correct page size for your printer before pushing the OK button.
