apropos – search the whatis database for strings
Summary:
This command will search the given string the Whatis database and list the matches on the screen. For example, the following command will list the available (in the whatis database) compilers:
$ apropos compiler
Read: man apropos, whatis
I think these are the basic help command you would really need. After these I would write about the other important commands needed to work your way through GNU/Linux system.