How to obtain a digital ID in Windows Mail

I have windows mail on a laptop computer and Windows Vista as the operating system. I want to obtain a digital ID and when I follow the pathway described in Help I encounter a roadblock. When I get to Secure Help under Tools and click on Digital ID I get a window with four tabs, and the Personal tab is highlighted. When I click on Import I get the set up Wizard and arrive at a request to nominate a file from my system. Questions: Is Personal the tab I should be selecting? If so what does the request in the sign up Wizard for a file mean and how should I nominate one? Is it the file where my Digital ID should be stored? If the Personal tab is not the correct one which tab dhould I select? Can anyone help?