VB 2008 Check For Data And Make The Program Stay There Until The Data Is Input?

I have a program for school project that has input fields for Name, Address, City, State and Zip. I need to error check so that the fields are not empty.I have used If statements that check to see if the fields are empty and shows a message box if they are but if I leave the whole form empty and click the button that activates it, all the if statements go- one by one instead of pausing for the user to input the required data.How do I check for data and make the program stay there until the data is input? I have tried TRY/CATCH but it won't catch this type of error.

this is the

'This program computes customer's bills at the pizza shop for all combinations of
'crusts, toppings, sizes and discounts
Option Strict On
Public Class PizzaForm

[code].....