VS 2008 Assignment help in visual basic

Hello

I have a visual basic assignment in visual studio that I am stuck on.
The assignment is to create a coffee shop system. I am give four drinks with fixed prices. The user inputs the orders and it should show the item amount, sub total , VAT and total due. Also I need to put a 15% discount if it is a take away. Then I need to have a summary command which is:
The user should be able to run a report at the end of each day that returns the average price per sale and the number of customers that were served that day. A running total must be returned for the number of orders taken.
The program should run for the whole day allowing the user to enter new orders. The summary statistics are produced at the end of the working day and should be output to a text file.

I thought of creating four buttons for each drink when clicked on it shows the item plus its price in a list box and add to the sub total. But I was told if I specify the amount of each drink then click calculate it would be better.
I know how to create the button method but the other on I don't.
I am stuck on almost everything in the coding especially the summary command.

I would appreciate any help I get