GPL Ghostscript isn't a program to use on its own. Rather, it's a helper that interprets PostScript and .pdf documents. For instance, some Adobe Reader alternatives require Ghostscript to work.
Often these files, such as CutePDF Writer, allow you to install Ghostscript as part of their own installation process. However, if you find yourself needing Ghostscript, you can download this one and install it with the instructions at Ghostscript.com.
Note: Vendor Artifex Software does not offer technical support on this free version of the software.