Dear,
Mainly historical orders are used to track the maintenance activities were performed in long back and not updated in SAP, so now just to have the total history of a technical object in SAP for reporting and analysis purpose, we sue this functionality.Transaction code is IW61.
Have you read the SAP help on historical orders? Pls have a look at below threads for better understanding.
PM: Historical Maintenance Orders - Release Notes for Release 3.0A - SAP Library
New Features of Historical orders:
http://help.sap.com/saphelp_46c/helpdata/en/e1/078ba835e1d311ba4d0800060d888b/content.htm
Entering cost in historical orders:
Entering Costs in the Historical Maintenance Order - Maintenance History (PM-WOC-MH) - SAP
Regards,
pardhu