The login name can be anything. It allows you to refer to it later so that you can have two separate logins (for instance user and admin).
The find record tab identifies how to find the user login record. The most common case is to find by username and password and bind them to the the username and password fields... but in some cases on intranet sites you may want to only use an email address to allow login, or in extremely secure sites you can use Username, Password, and an additional key of some sort.