Linewrap in Org-mode of Emacs?

The default mode for org-mode is truncate-lines mode.

You can customize this behaviour with org-startup-truncated. Type F1-v org-startup-truncated for a description, and then click on the customize link to change it.

You can also toggle it on-the-fly with the command toggle-truncate-lines, between the normal Emacs view and the normal org view. For example, use this:

(define-key org-mode-map "\M-q" 'toggle-truncate-lines)

M-q is bound to fill-paragraph by default, but probably you don't want to use it within org-mode.

Org mode does not wrap lines on purpose, to not make tables appear very ugly. The function org-fill-paragraph controls the insertions of line breaks for one paragraph for you. So you might want to use that instead of line wrapping.