How to make a Cashier Program in excel?

Hi! My name is Regie. I want to learn how to create a program in excel. I am using MS Office 2010.
My Boss want me to make a cashier program using microsoft excel.
I only know use excel a little bit.
Do you know how can I make one? The outcome is should be this;
1.)I insert the serial code.
2.)the price will come out,
3.)Insert Quantity.
4.)Total will come out.
5.)Insert Payment.
6.)Balance will come out.
Inside the software was:
1. Serial No = 7614500070013
2. Item = From Eternity to Eternity (Book)
3. Quantity = 5
4. Quantity Sold = 2
5. Quantity Left = 3
6. Original Price = 20.00
7. Sales Price = 25.00
8.Invoice No. = INV00914
I was totally lost. Can anyone of you guys help and teach me how to do this.? I will be glad if someone can can send me a full details and step of tutorial to make this program in my own risk w/ your guide of help.

Many Thanks in Advance.