The general ways of managing inventory are as below:

1) Allocate a stock code for each product he carry.
2) Issue a stock in for stock purchase. The details for a stock in are from which supplier he purchase, when the purchase is made, quantity & cost.
3) Issue a stock out for stock sold. The details for a stock out are when to whom the sales is made, when it is made, quantity & selling price.
4) Have a stock flow which act like a report to track your stock level. It is a computation for all his stock in and out for a certain period of time.

He will also want to handle situation like stock return, stock spoil, stolen stock & issue stock in/out depending on the situation.

This post has been edited by ListenToTheAngin: Jan 1 2017, 11:10 PM