Normally, the man pages are installed when the operating system is installed, however some system administrators choose to remove the man pages to conserve space. While the man pages do take up some disk space, it's generally not a good idea to remove them. Contained with the man pages are descriptions of the commands themselves, along with their proper syntax, options and arguments the commands will accept. To look up a man page for a specific command, type man followed by the command you're interested in at the shell prompt. Man pages are formatted such that you are shown only one screen of information at a time.
Some man pages can be quite lengthy.
Once you've read the first screen, tap the space bar and the second screen will appear. As helpful as man pages are, the man command requires that you know the command you're looking for. When you're just learning UNIX, there's a much greater chance that you may know what you're looking for, but you don't know what it's called. In this case, UNIX provides two other tools that are invaluable. Apropos is a command that will tell you about UNIX commands.