Absolutely - Linux is an alternative (though less-popular) operating system to Windows.
Linux
The question is unclear. Assuming you are asking usages of linux, well people use it for personal computing. Most of the companies use linux for servers. A Linux based system is free for anyone to use. A linux system distribution can be used in the same way as windows. Almost any application for windows has an equivalent application available for linux that does the same job. Linux has word processing, picture, sound and video edotors as well as their file format converters. It can be used to play many games, play song, watch videos. Linux is available for almost any personal computer available and almost any other computer in use. Most commercial network routers and firewalls are based on linux.
No. Linux also runs on mainframes.
A PC is a Personal Computer, doesn't matter what the operating system is necessarily. Could be Linux, Windows, etc. The only distinguishing factor is the Mac.
Windows and Linux use device letters to identify each storage device on a computer.
If you want to share files with other linux computer use NFS. If you want to share files with windows computer use SAMBA.
Windows: Open start menu, click "Run", type in "telnet" Linux: Open a Terminal window, type in "telnet"
Linux Ubuntu and Apple Mac OS
Yes, Linux is like an operating system much like Windows OS or Mac OS. Linux is kind of like a community of Operating Systems. A popular OS from Linux is Ubuntu.
yes Macintosh, or Mac, is a computer made by Apple. "PC" stands for "personal computer", meaning it could be a Windows, Mac, or Linux computer.
Windows and Linux use a device letter to identify each storage device.
A PC is a Personal Computer. A Mac is a personal computer. A Mac is a PC. A Mac with an Intel processor can run the Windows operating system (or Linux or many others) if needed.