Usually included with PC purchase. Usually purchased separately from the hardware. Latest version usually included with new Macintosh purchase. It is a widely used operating system, particularly for the World Wide Web. Comes in many different flavors, one of which is Linux.
Prices range from free to hundreds of dollars.
Some derivatives have graphical user interface, but, generally speaking, Unix flavors are definitely not for newbies. Linux operating system is free. However, it is not for the new PC user. There are a lot of codes and commands you need to understand. It is the fastest-growing operating system in the world.