The man command which is short for manual provides in depth information about the requested command or allows users to search for commands related to a particular keyword.
syntax: man [-] [-k keywords] topic

Shows you online manuals on Unix commands.

- Displays the manual without stopping.
-k keywords Searches for keywords in all of the manuals available.
topic Displays the manual for the topic or command typed in.

Example:
man mkdir - Lists help information on the mkdir command. man -k irc - Quickly search for manuals containing irc within them.