I have been using PCs since 1994, learning as much as possible by trying everything in the OS and all the programs I had.  A click here, a click there and my PC would crash.  After learning how to re-format, re-install the OS, and get everything working I was safely able to practice my knowledge and continue the search for new features.  Basically I learned everything about Win 95, HTML, Word 9x, etc. by playing around.  This is what I think is the only way to learn about a PC or MAC =).