Nice tip rudge12000. In the same vein, if you know what you want to do, but can't remember the command, at the command line, type "apropos [keyword]" (without quotes), where [keyword] is the string that relates to the command you are searching for.
[mokmeister@localhost ~]$ apropos whatis
apropos (1) - search the whatis database for strings
- Create the whatis database
whatis (1) - search the whatis database for complete words