how do i use web.config for authentication and authorization?

Question

I am new to asp.net. I want to use wb.config for authorization and authentication.

Consider a scenarion where i grant access to the Kim identity and

members of the Admins role, and denies access to the John identity and to all anonymous users:

<authorization>
  <allow users="Kim"/>
  <allow roles="Admins"/>
  <deny users="John"/>
  <deny users="?"/>
</authorization>

can any1 tell me where does these users and roles are defined?

from where this kim, Admins, John are compared with while authorizing?