The Help menu is cleverly hidden in plain sight.
One thing to note: if you have an active Internet connection, selecting the Help menu will often trigger a pause -- sometimes a lengthy pause -- as your Mac looks out across the Internet to see if any of the documentation needs to be updated. This is good: your documentation is self-updating. But it can be disconcerting if you are expecting an instant response.
Because the Help menu is available globally, Apple has encouraged developers to use the same mechanism for their own programs. This can quickly amount to a fairly large library: not only do you get the standard Mac OS X help files, you'll also see the Developer Help Center (if you've installed the optional Developer Tools), plus help libraries provided by various commercial, shareware and freeware authors. One noteworthy holdout: Microsoft does not use Apple's Help menu. Instead, their documentation -- for Internet Explorer, Word X, PowerPoint X, etc., is handled according to Microsoft's guidelines, not Apple's. One major downside to this: you must actually be running one of the Microsoft programs to read the documentation. In contrast, you can read about AppleWorks, for example, without actually opening the program.
Depending on what you have installed, your Help menu might be limited to the Mac OS X basics, or include topics related to the optional Developer Tools CD-ROM, or have entries for various other software packages you've installed.
Help in the Unix world is available through "man" pages. There is actually a program within Unix called "man" that searches through its own databases to find relevant documentation on various Unix commands. So, for example, if you wanted to learn how to use the command for listing the contents of a directory, you would type:
which would give you pages and pages of information on how to use this seemingly simple but very versatile command.
The "clear" command isn't very exciting, but its accompanying man page is one of the shortest. Some commands have man pages that, if printed, would equal good-sized books.
Naturally, the man command itself has a man page, and it is well worth a look. As with all documentation, it is best to learn how to read the documentation before you find yourself armpit deep in a crisis.
There are a fair number of "alpha geeks" who claim that all computer books are, by definition, out of date: by the time a book makes its way to press, the technology has moved on. With this as their guiding principle, they never buy books, calling them "dead trees." Instead, they spend endless hours hunting down obscure Web sites, looking for information, and killing entire forests as they print out Web pages, man pages, PDF files and other forms of formerly electronic documentation. These pages are briefly skimmed, then trashed.
If you find utility more valuable than irony, give some thought to visiting a large bookstore, and checking out the computer books section. Almost any decent sized bookstore has a computer section today and, once you manage to wade through the Windows riff-raff, you'll discover there are wonderful books available on almost any computer topic, from how to use iPhoto to how to write programs in Cocoa for Mac OS X. Unlike electronic documentation, you can stick bookmarkers in books, you can open up several books at once -- with the computer turned off, even -- and compare them, you can write your own notes in books, you can read them on a bus or a train, and you don't have to go through special security precautions to take a book on a plane.
Don't expect printed documentation to make a comeback. But do learn how to use the available electronic documentation, and check out your favorite local bookstore.