Hi,
There are plenty of documents out there about ESS customization, have you checked them?
http://scn.sap.com/community/erp/hcm/blog/2012/03/29/launch-pad-customization-in-sap-essan-overview
http://tagiltsev.blogspot.fr/2013/03/ess-mss-customization-in-ehp5.html
If you have, what is the particular problem you are facing?
Best regards,
Guillaume