1. Teach the ordinary sale and stop
On the first day, teach exactly this: find the item, enter the quantity, pick or skip the party, take payment, print. Nothing else. Returns, quotations, purchase entry and reports can all wait until the basic transaction is automatic. Staff trained narrowly are billing unaided after one session; staff shown everything are overwhelmed after three and go back to writing slips.
2. Let them do it, not watch it
Demonstration teaches nothing. Have the person bill real customers with you standing beside them from the first hour, correcting as it happens. Twenty real bills teaches more than an hour of explanation, and it also surfaces the specific things they find confusing — which are rarely the things you expected.
3. Give a limited login from day one
Billing and receipts only. It removes the fear of breaking something, which is what actually slows a new person down, and it removes the temptation to hand over your own password. Add permissions as they earn them; starting broad and pulling back never happens and creates resentment when attempted.
4. Language is not a detail
A screen in English is where a person who has kept a register for fifteen years stops. In Hindi the same person is billing unaided after one session. This is the single largest factor in whether shop software survives contact with the counter, and it is the one most often overlooked when the owner — who reads English comfortably — chooses the product.
5. Watch the first fortnight, and say so
Look at the audit trail and the per-user day-end for two weeks. Early mistakes are training gaps, and finding them in week one costs almost nothing while finding them in month three costs a customer. Tell the person on day one that entries are attributed — it reads as normal then and as suspicion later.
6. The mistakes to expect
Three come up with almost every new biller. Selecting a similar-looking item rather than the right one, which barcodes largely solve. Recording a credit sale as cash or the reverse, which shows up the same evening if you close the cash book. And forgetting to attach the party on a credit sale, which leaves the ledger short. All three are training, not character, and all three disappear within a fortnight if they are caught early.