The most commonly used program is Microsoft Word, so that's what you'll need to find a book about. Assuming that you've got Word on your PC, it might be best to find a volume that matches the edition of the program. (e.g. If you've got Word 2007, it would probably be best to find a book specifically about that program, rather than one which deals with an earlier or later version of Word. However the basics of word processing are the same across all versions of Word, so you can still use a book about Word 2003 to get to grips with most of what Word 2010 does). So it's hard to recommend a specific title.
The 'Bible' series is excellent but fairly pricey. Here's the version for Word 2003:
http://tinyurl.com/32omxko
The 'Dummies' series is quite popular (but the pace is too slow for my personal preference). Here's the version for Word 2007:
http://tinyurl.com/3andgbj
Colleges might incorporate word processing and touch typing skills into a single course, leading to an RSA (Royal Society of the Arts) qualification. If a course in word-processing on its own was offered, it would probably be as a module of the ECDL (European Computer Driving Licence):
http://www.ecdl.org/index.jsp?p=93&n=98
Chris