No, you don't substitute that line with the usernames and passwords.

Since it's never been clear, I'm assuming your program asks the user to enter their username into a textbox and a password into a different textbox. What are the names of those textboxes?

Assuming the names are txtUsername and txtPassword, respectively, then the line of code should be EXACTLY:

Code:
Login(txtUsername.Text, txtPassword.Text)
That calls the Login Sub in your module and passes the values typed in to the Username and Password textboxes to the Sub.