What an entry records
The supplier, their invoice number and date, each item with quantity, rate and GST, and any freight, loading or unloading charge on the load. That is it. The item lines raise stock in the unit the item is held in, so a purchase in tons against an item held in kilos converts on the way in. The GST on the bill becomes input credit against your return rather than a number you have to find again later.
Freight belongs on the purchase
The supplier invoice is not what the stock cost you. Freight, loading and any shortage on delivery are real, and in bulk material they are a meaningful share of the total. Recording them on the purchase produces a landed cost that is higher and more honest than the invoice value, and that is the figure your selling rate should be set from. Pricing off the invoice value alone is the commonest reason a shop finds its highest-turnover line was also its thinnest.
Your side of the ledger
Suppliers get the same treatment as customers — bills raised on you, payments made, balance outstanding with its ageing. When a distributor statement arrives you compare two records instead of trusting one, and the differences surface immediately rather than being carried forward for three months. It also tells you how much of your working capital is actually your supplier's.
Purchase rate against sale rate
Because both sides live in one system, you can see per item what you bought at and what you are selling at. Rates move — steel weekly, cement seasonally — and a selling price set three months ago against a purchase price that has since risen is how a shop stays busy and stops making money. The comparison is a report rather than an exercise, so it actually gets looked at.