How does SharePoint automatically logged a user in?

Hi guys,

Here is the steps for automatic logged in sharepoint site when open it.

(1) Open IE browser.
(2) Go to Tools->Internet Options.
(3)Click on Security Tab.
(4)Click on Trusted Sites.
(5)Click on Custom Level. So security settings pop up is open.
(6)Go to User Authentication tab and select Automatic Logon with current user name and password.