Following is the step by step procedure to config loans
1. First Create Loan Types
2. Do Country Assignment
3. In the section "Technical Attributes" enter the loan category (for ex: Annuity Loans)
4. In the section "Conditions" enter the Debit Interest and the govt. ref interest rate and assign the loan type to period parameter
5. Edit the feature ALOAN, 40LGR and 40LSL as applicable
6. Maintain Loans Eligibility Checks and Limits
7. Maintain Loans Disbursement Schedule
All the above would appear under LOANS config section in SPRO.
Once the configuration is done, maintain the the infotype 0045 and also ensure that loan details are configured in the PY slip (as per ur requirement). Perks calculation will be taken care by system based on the interest rate and ref. interest rates provided by you.