b22222c :
there is only one variant of linux? Where i can downoad? (I understand about windows but zeroabout linux). Thanks
No, there are hundreds of different Linux distributions that do things a little bit differently. for example, Red Hat, Debian, Mandrake, Mandriva, Ubuntu, Debian and Mint. If you just want to be able to play with this POS system, I would go with Ubuntu or Debian. Ubuntu is desktop oriented, fast and has a very large number of packages. Debian is server oriented, fast, and has a HUGE number of packages. So it is likely that you will find this POS system prepackaged for one of these two distros. I would start with an Ubuntu LiveUSB or LiveCD, boot, and before even installing you can play with the Ubuntu desktop as well as their package management tool called apt-get:
http://www.tecmint.com/useful-basic-commands-of-apt-get-and-apt-cache-for-package-management/
If you don't find it in the available Ubuntu packages, you can check the Debian package database and see if it's there:
https://www.debian.org/distrib/packages
If it's there then you could just go ahead and install Debian.
If for some reason it's not in either of their package management systems, then you could go ahead and follow the instructions on the POS docs (from the website or wherever) for installing the POS system on a distro that doesn't have it already packaged. Once you've played with the POS system enough, if you wish to deploy this on multiple machines, you will probably want to consider a prepackaged solution.
https://www.debian.org/
http://www.ubuntu.com/