12.2.1 GnuElpa

“GNU Emacs Lisp Package Archive—The default package repository for GNU Emacs.”

• http://elpa.gnu.org
• Browse the Repositories
• The Gnu ELPA Repository
• Gnu ELPA Project Page

This should already be in Emacs (for Emacs 24+):

package-archives

(setq package-archives '(("gnu" . "https://elpa.gnu.org/packages/")))

You can also add repositories one at a time:

(add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/"))
(add-to-list 'package-archives '("org" . "http://orgmode.org/elpa/") t) ; Org-mode's repository

To use it, type ‘M-x list-packages’ in Emacs.

Since you’ll probably want to use your installed packages, it’s also recommended that you add (package-initialize) somewhere in your $HOME/.emacs file.