Many of your basic questions could be easily answered using the Cow’s search engine. However, in the interest of preserving you from having to do any effort on your part, here is a quick example which may help you understand the difference…
Linear editing: Example: Roll a tape, find a section you want, record it to a place on a time line on another deck; roll first tape, find another sequence, record it to the 2nd deck, etc. (Think a linear, start to finish process)
Non-linear editing: Using software, you can import footage onto a harddrive and edit pulling from anywhere at any time from your files. It does not have to be as in the linear fashion where you have to rewind a tape to get back to a point which you may want to pull footage from. Using non-linear, you can grab anything from anywhere at any time in your project, as it is all available to the editor. Hence, non-linear.
Far from a perfect answer but the example holds.
Ron Lindeboom