Add the following lines to your .emacs file. The last four lines define global keys for some commands — please choose suitable keys yourself.
;; The following lines are always needed. Choose your own keys. (global-set-key "\C-cl" 'org-store-link) (global-set-key "\C-ca" 'org-agenda) (global-set-key "\C-cc" 'org-capture) (global-set-key "\C-cb" 'org-iswitchb)
Files with extension ‘.org’ will be put into Org mode automatically.