Ticket Details is for adding fields to tickets. The other way that you can do it is via help topic.
Contact information is for adding fields to users/clients (NOT tickets).
What specifically isn't working? (please provide screen shots)
What I was trying to accomplish, was that a user, would enter in their site username, when register on the support site. Then when they create new tickets, the username would be automatically inserted. I put a field in the contact information template, and enabled it to be required etc. However, unlike name and email, it doesn't populate. Only way to make it appear inside the ticket, is to also put it within the ticket details template as well. When you look a user up, it also does not display their username info, as I thought it would, either.I have attached a few photos.