All the pieces of GNU software were available for free download and were therefore free of charge. But this brought its own problems. Not everyone had the know-how to put all the bits and pieces together into a complete operating system. Those who could do this didn't necessarily have the time for it.
Because of this, a number of companies stepped in to do the hard work. They put together versions of Linux, complete with all the software from the GNU Project, which they then sold for a fee on floppy disks, CDs, or DVDs. They also added in bits of their own software, which made it possible to install Linux easily onto a computer's hard disk, for example. They produced their own manuals and documentation, too, and did other things such as bug testing to ensure it all worked well.
What they came up with became known as distributions of Linux, or distros for short. Examples of these companies include Red Hat, SUSE, Mandrake, and many others around the world. Additionally, a number of hobbyists got together and formed organizations to create their own distros, such as Debian and Slackware.
Modern distros are very advanced. They make it easy to install Linux on your PC, and they usually come with everything you need, so you can get started immediately. Additionally, they have their own look and feel, as well as unique ways of working and operating. This means that SUSE Linux is not the same as Red Hat Linux, for example, although they share a lot of common features and, of course, they all share the core GNU software.