Home page is made of gkGrid module. This module loads other modules attached to different positions. Please check which position your gkGrid loads - and find correct one - edit it with tineMCE disabled and create a link to your facebook/google/twitter page.
For more informations please check the documentation:
http://www.gavick.com/documentation/joo ... k5-module/"where get it the modul from" - sorry this still is unclear to me.