There are several ways to secure-erase your hard drive (e.g. SATA or SSD) before selling, gifting or otherwise disposing of it. Here are a few methods:
Writing/burning an ISO file to create a bootable USB drive could be done using RUFUS, a free utility. You can find your particular version of RUFUS here https://rufus.ie/en/ (the easiest way to select and download your appropriate version of Rufus, and some instructions for its use) and here http://rufus.ie/downloads/ (the more complex page to select your appropriate download, and without any instructions).
Writing/burning an ISO file to a CD or DVD could be done using various applications and utilities, such as BURN AWARE FREE found at https://www.burnaware.com/ and the download page https://www.burnaware.com/download.html. Please understand the difference between downloading the FREE VERSION of BurnAware versus the Free Trial of the paid version of BurnAware.
You can download DBAN Here: https://sourceforge.net/projects/dban/
If you buy Parted Magic, this describes how Parted Magic performs secure erase: https://partedmagic.com/secure-erase/
To securely erase a disk involves overwriting all disk sectors multiple times with anonymizing data, such as writing zeros to all sectors on the first pass through the entire disk, then writing all ones on the second pass, and writing randomly zeros and ones on a third pass (or overwriting with other secure sanitizing sequences, such as 7 passes rather than 3).
DBAN has its own boot environment (no need to install it on an existing operating system) so you can use it to securely erase the boot drive or other data drive on a computer without first removing that drive and installing or attaching it to another PC. Caution! Be extremely careful when using DBAN so that you don't accidentally wipe the wrong drive.