Hi Pradip
Please find the below link of the LSMW process.
LSMW:Upload Master Data Using Batch Input Recording Part 1
If you are implementing ESS/MSS then OM is compulsory module for it because OM is used in ESS/MSS for reporting purpose e.g. If Manager has n no. of direct reports the ESS/MSS will fetch data with help of relationships defined in OM.
I hope this helps.
Regards
Rahul