About Roles and users

Question

I didnt met with the login form in .net. Here i want to create logins for four users and the i have a masterpage in which i hav menu items that describes all the forms of application.Now i want to hide some menu items from users other than "admin"...how i can set that login credentials..am new to this so plz help me with some links and articles where i can easily findout.Please help me with reply...Thanks.....