Just double click the Hard Drive Eraser exe file and select a drive (this is the main defect of this program. There is no option for erasing data from the whole hard drive; you need to select individual partitions one by one.), select a shredding scheme (DoD5220-22M is recommended scheme, Gutmann is more secure, but processing is slow) and click on ‘start’ button.
Why this program? Just formatting a hard drive is not able to destroy all data. It is very easy to recover all data using either commercial solution or one of applications for data recovery. So, for a security reason, this type of tool is necessary when discarded hard disks.