Using this tool is very simple. Download it from http://www.acelogix.com/regbak.html. Run the exe file (no installation required). Select a destination folder. The default backup folder created is 'Regbak' inside your 'Windows' folder. Now, select the 'Registry Hives' to backup. By default, the 'System' and 'Current User' hives are selected. You can instruct the program to backup the rest of the hives also by enabling the 'Other Available Hives' option.
Now click 'Next'. This will take you to a confirmation page. Click 'Start' to begin the backup process. After successfully saving the Registry files, click 'Cancel' button to close the program. Also, you can go to the folder where the backup was made by clicking the path shown.