Hi Rahul,
I assume, in a process when your supplier deliver goods, you generate a purchase order, purchase invoice and pay. To get it done in ERPNext, you can follow these steps:
step 1: Make a purchase order (Buying > purchase order)
Step 2: Make a purchase invoice (Accounts > purchase invoice) by selecting "from existing purchase order" from "Actions" from top right. This step will add all goods price delivered by your supplier in whole month.
Step 3: At the end of month you can open that "purchase invoice" and make a payment entry by clicking on "Actions" button from top right.
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Sunil
Partner for ERPNext