Dear Rakesh,
1. If you would like write a any PCR first you should understand their business process and need to be written in SAP.
2. There are so many PCR's & scenarios, (where based on Business process PCR's will be written)
3. If you would like write any PCR based on client requirement first you should know like for this requirement which Operation need to be used. (For finding total operation's Go to PE04 and find relevant Operation)
PE04 Operations:
http://www.sd-solutions.com/SAP-Payroll-Schemas.html
Sample PCR:
Ur's Mohan