You aren't supposed to MANUALLY enter anything except in the 'Field Value' field, which is where you put the value that you want auto populated - ie, the password, for a password field, or the username, for a username field.
If you read the directions (the text above the field boxes), you will see that all you have to do is click in the field directly on the web form and it automatically populates the 'Field Name', 'Field Type' and' 'Form Name' fields. I believe that it will also populate the 'Field ID' field, but I'm not sure. I've never used it, nor needed to ask about it...
Eric?