SHELL

bash manual

man <cmd> 		# for manual of <cmd>, i.e. complete documentation
<cmd> --help  	# for optional parameters
<cmd> -h		# short version of help

apropos <keyword> 	# search for short description for matched instances
					# of the given keyword

apropos sudo		# an example

bash manual command

man command #get manual instructions of a command
#Example
man ls