No need of computers or internet. Easily use your phone for stock tracking.
Record the buying price and quantity of items purchased on the Stok app whenever you purchase an item in your shop. Then after a period of time you are comfortable with (daily, weekly, monthly), record the selling price and the number of items sold during that period of time. Stok will in turn keep track of number of items in stock, profits , losses, buying and selling history, the buying price per item so that you can easily compare and adjust the selling price and finally a change in the buying price of a product so that you can also adjust the selling price if need be.