CentOS is one of the most stable operating systems I have ever worked with. You can easily download it from official mirror sites that provide the disk-image file for free. The list of mirror sites can be found in Distrowatch.com as I described in my earlier post.
After downloading the image file (typically the have .ISO extension), you can burn it on a physical disk or you can create a bootable USB Drive, and boot your system with either of these two ways.
When You boot your System with the bootable media, your will face this welcome page: