Difference between help, info and man command

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help

is a bash command. It uses internal bash structures to store and retrieve information about bash commands.

man

is a macro set for the
troff (via groff) processor. The output of processing a single file is sent to a pager by the

man

command by default.

info

is a text-only viewer for archives in the info format output of
Texinfo.

help

is a

bash

built-in, providing help for

bash

commands only

man

is the traditional form of help for almost every command on your system, and not only, sometimes also configuration files have their own man page. In Linux distros organized in packages, the relative text is in general provided from the
same package providing the command. If you have

bash-completion

you can take advantage from
TAB to see what man pages are available.

info

is an alternative system to provide manual pages for commands, based on

GNU emacs

. It is provided mainly for

GNU

commands and utilities. It don't seem to be widely adopted from others.