I actually got to know Unix with a little paperback reference book: http://www.amazon.com/Pocket-Guide-Unix-Michele-Petrovsky/dp... After you learn the "unix basics" the most valuable thing I found was reading the description of every single common Unix command. I'm pretty sure I also had a small pocket reference which had the same information in a more compact form, and I found myself reading that everywhere I went. Here's a similar book from O'Reilly: http://shop.oreilly.com/product/9781565924277.do
Here's another little guide which goes over all the general topics: https://docs.google.com/viewer?a=v&q=cache:4oBqPlq1f7oJ:...