Linux makes up many Operating Systems, all of which are free and available for everyone. The reason for this is that they are Open Source. Open Source means that the entire product is free for legal distribution by anyone. For example, I could legally send you a CD with a Linux Operating System on it. However, that does not mean that someone could sell it without giving credit to those who made it. This allows a free flow of products and information without taking away the producer’s rights.
Due to the fact that all Linux Operating Systems are Open Source, many versions, or Distros, (short for distributions) have cropped up. These provide unique aesthetics, looks, feel, pre-installed programs, and anything the creator wishes to include. This is much like Android. There are numerous versions and sellers of Android, and all of them provide different aesthetics, layouts, and support that come with them. However, they can all be made to function exactly how the user wishes them to. This is due to the fact that Android is actually a version of Linux! If the core code that Android is based on was not Open Source for everyone to look at, modify, and use, than there would only be one version of Android, much as there is only one version of Windows. This is what Linux actually is. It is the base code that all Linux distros use and customize. And just like there are numerous versions of Android, there are numerous Linux distros. So many in fact, that it can be difficult to decide which to use. However, the benefit of having so many distros to choose from is that a distro can be found for almost anybody. The hard part is finding it.
Thus, you will want to choose a Distro that suits your needs.