Unix provides a rather robust help system supported by the command "man". This command is smart enough to search through specific directories where documentation about various Unix commands are located. Collectively, these files are referred to as "manual pages" or just man pages for short.
Remember that every Unix command is actually a small program on the system. This means that the Manual page must be written for each command. If a programmer has done a complete job of software development, the command will conform to Unix/POSIX standards and will also have an appropriate man page for it.
Manual pages are broken up into sections. The first section gives the syntax of the command. This explains how the command should be entered. The next section describes the command's functionality, and the next section describes what options (flags) may be used to set or perform various features of that program command.