Use the automatic installer in your WordPress dashboard >  plugins > add new.  Search for Speakout! follow the instructions. Or you can:
  1. Download the zip file from the plugin’s respository
  2. Unpack the file
  3. Upload the “speakout” folder to your “/wp-content/plugins/” directory
  4. Activate SpeakOut! Email Petitions through the “Plugins” menu in the WordPress dashboard
  5. Add a petition