Linux Operating systems or “distros” are available for download from a variety of sources. When downloading a distro, I usually go to distrowatch.com. At other times I go to the project’s website; for example: Linux Mint, Crunchbang, and Ubuntu.
Why go to distrowatch? It’s an easy name to type into a web browser. It lets you search by distribution name and takes you to the “project page” for that distro—where you can get details about the distro—such as country of origin, which releases/editions are available, what software/applications are included, the default desktop manager, and more.
When your download is complete, you should verify your download before you burn the .iso file to a CD or DVD. Verification is the process where you compare the md5 hash of your downloaded .iso with the expected md5 hash published at the website where you downloaded the .iso from.
There are a few ways to verify a .iso file. In linux, issue the command md5sum [path-to-iso-file] and press ENTER. For Mac OS-X, follow these instructions. Lastly, in MS Windows, follow these instructions.
After verifying the download, burn the .iso to a CD/DVD. Just make sure that you’re burning a “bootable iso image” (which is different than creating a data CD that includes the .iso file). Most of the good burning software will have the option to “burn an image to disk”.