selecting a page according to the selected item from drop down list

I am newbie to asp.net. I am using ASP.NET, C# for creating a website.
i've a dropdown list in my login page. The dropdown contains three items:
admin staff pubic the user fills the login form & selects an item from the dropdown list. After clicking on the submit button, the user should be rendered to the page according to the selected item from the drop-down list.
i.e. if the user selects the staff item he/she should be rendered to the staff page "staff.aspx" page. before that all the links in the login page should be disabled.
how can I do it?
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in registration page I've to insert the role of the users. I've made a dropdown for it in my webpage.
admin staff public but in the database these ...