I want to try transaction OOOS .  How actually does it works?

I have a entry  like this

PA20  PD10  S     RHRHAZ00    PA-REPORT-START_SKIP

What is PD10 where I can find this request code.

I'm not sure what you're asking but if you want the user menu path that will give you the same report:

HR -> OM -> Tools -> Database -> RE_RHRHAZ00 - Display DB records

and

Check out OSS note 87867 for some info related to OOOS.