Nice basic introduction. For anyone wanting a comprehensive overview of each command, with examples (and generally more readable than man pages), the computerhope site is good. For example here's wc:
It's UN*X. The one thing it actually does good is having documentation on the system, instead of some weirdo's web page covered in ads. Type man <cmd> or info <cmd> in the shell. Also, for most of the world population, this will be a few seconds faster since it avoids loading a web page.