This is a Recruiting page. To edit the content, browse to the slug 'spread_the_word' in the Control Panel, then click on the Intro tab under Recruiting settings. You can also modify the settings of the Recruiting, including default text of a tweet and the page you are promoting, in the Basics tab under Recruiting settings.
Spread the word
Non tracking link
When you sign in, you will be able to see who you've recruited here.