User ID is the name or number that you use, in combination with your password, to log into Account Manager.
You can customize your User ID by logging into Account Manager and selecting "Profiles & Accounts" then "User Profile" from the left-hand navigation, and then clicking the "Edit User ID/Password" button.
If you wish to be automatically logged in every time you return to http://www.networksolutions.com, be sure to check the "Remember me on this computer" box when you log in.