Sun co-founder John Gage, who coined the phrase "The Network is the Computer" which later became a Sun slogan, is today entirely correct. Oh sure, he's not semantically correct, but he's basically correct in that the true power of the computer is not realized until it is connected to something. MP3 players are little computers that are networked to your computer long enough to load music on to them, for example. One useful and basic thing we can do to cause computers to participate with one another is to copy files between them. Sometimes it's most effective to just do this with a disk, but if they are connected to a network, it's usually easiest to copy the files that way, if not fastest.
If you are looking for an introduction to Unix, this is the book you're looking for. If you're looking for an introduction to ANSI C, again, this is probably the book you're looking for. If you want one book that will introduce you to both, well, this is the only book you want.