Emacs package manager is provided and the mirror

 

Add in the init.el

 

(require 'package)
(add-to-list 'package-archives
             '("melpa-stable" . "https://stable.melpa.org/packages/"))
(package-initialize) 

course url may be provided inside the mirror China; Reference: http://elpa.emacs-china.org/

 restart after Emacs can use the 

command such as the installation mode can use the following markdown

Package RET markdown the install-MX-MODE RET 

M represents the alt key, and the Enter key is RET 
Reference: 
https://jblevins.org/projects/markdown-mode/ 

For use the shortcut keys associated packages markdown generally ~ ctrl c is the start key combination. Is not this also the other modes