man stands for manual. The closest thing to compare them to in a Windows world would be a Help File, but man pages tend to be more thorough and complicated than Microsoft's Help Files. When in doubt about a command or its switches, consult the man pages.
Common ways to consult man pages include looking them up on the web, for example at freebsd.org's Hypertext Man Pages, or using the man command to view them interactively from your shell.
man automagically gets passed to your default pager, more (which is really less,) so you don't have to worry about the text scrolling past your console.