UNIX: Finding out for yourself
If you already know the command to use, the most helpful thing to do is to use the command man X where X is the command you know. It will (should) tell you everything you need to know. See, for example man ls and man cp and even man man. >
Man pages are available in many places on the web, search the web for "UNIX man pages"
Proviso: Some man pages are really, really bad (tar springs to mind). Some are really out of date, and some others (mainly for GNU programs) just refer you to the info page (use the command info X).