Suganth,
I don't want to give more brief information about it. Because, Already Balajee was described you more information about how to start and where to start.
My advice is , in open market place available on SAP best practices for EHS . find the below link.
http://help.sap.com/saap/sap_bp/EHS_ERP605_CN/HTML/Content_Library_EHSM_EN_CN.HTM
Start to download and have a look all available scenario overview. start to practice as per business scenario.
This is the best way to understand the process
Edward