man is Unix's built-in help command. Help can be obtained about most Unix commands by typing:
If you want to see if there is a command that does something in particular, you can have it display a list of commands by key word specification. Type:
man -k keyword
where keyword is the keyword you'd like to search by. The man command will print out a list of commands that are associated with that keyword as well as a brief description of those commands.
If you are in X Windows, you can use "instinfof" as well. Check "helpme instinfo" for more info.