You want to know everything about an operating system ,and everything it is used for in one post? the scope of what you're asking is mind bogling.
Google will be by far a better source of information. www.google.com/linux
Personally though, i love it, i love learning, and this is a new challenege to tackle and over come. It can be used in anything from embedded devices to a desktop workstation to a server. It is highly configurable, so there's no 'settling' if you want something done, chances are it can do it, with enough time invested.