Website test: Pasing parameters to an input in a HTTP Post

Hi All

I have just started using SoapUi this morning and I am trying to build functional tests for my companies web application UI
My first task is to test a login form which requires a username and password as inputs in the form.
I am providing data to parameters via an excel sheet data source and then step through a login/logout process for each username/password pair provided in the excel sheet.

My question is how do I pass the parameters into the form input fields

Thanks for your help
Col