>> planning to Learn functional modules
Unfortunately, gaining functional knowledge as well as technical knowledge will come after getting your hands dirty on the job. Peoplesoft is such a complex architecture and there are no shortcuts to learning its modules.
Peoplbooks are always a great place to start. However, reading with no practicing will not get you far. As we all know, if you don't use it you lose it.

Another way to Learn PeopleSoft Functional is to get training from Mentors. that would help you to gain basic concepts and in-depth knowledge

I'd highly suggest learning to use the query tool because 1) it will help you understand the file structures of how & where the data is stored and 2) half of the errors we run into with payroll could have been prevented by running one of our dozen or so pre-payroll queries and resolving missing data fields (pay group, empl class, mailing address, tax data, benefit plan, etc) prior to running the Pay Calc or even worse the GL Posting once the payroll was already confirmed and we find a missing chartfield (funding source) or something that cannot be easily resolved.

With payroll, you must review the error messages frequently after each calculation and before you confirm anything. Don't rush it and please don't choke your technical support when the functional users forget to enter data. We're just here to help. :)